Revista Mexicana de Fitopatología ISSN: 0185-3309 [email protected] Sociedad Mexicana de Fitopatología, A.C. México

Félix Gastélum, Rubén; Mircetich, Srecko M. Influence of flooding duration on the development of root and crown rot of lovell [ persica (L.) Batsch] caused by three different species Revista Mexicana de Fitopatología, vol. 23, núm. 1, enero-junio, 2005, pp. 33-41 Sociedad Mexicana de Fitopatología, A.C. Texcoco, México

Available in: http://www.redalyc.org/articulo.oa?id=61223105

How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Revista Mexicana de FITOPATOLOGIA/ 33

Influence of Flooding Duration on the Development of Root and Crown Rot of Lovell Peach [Prunus persica (L.) Batsch] Caused by Three Different Phytophthora Species Rubén Félix-Gastélum, Universidad de Occidente, Unidad Los Mochis, Departamento de Biología, Blvd. Macario Gaxiola y Carretera Internacional s/n, Los Mochis, Sinaloa, México CP 81223; and Srecko M. Mircetich, Agricultural Research Service, USDA, Department of Plant Pathology, One Shields Ave., University of California, Davis, California, USA 95616-8680. Correspondence to: [email protected]

(Received: August 10, 2004 Accepted: December 24, 2004)

Félix-Gastélum, R., and Mircetich, S.M. 2005. Influence of minimize losses of peach trees due to root and crown rot flooding duration on the development of root and crown rot caused by Phytophthora sp. and P. megasperma, but it would of lovell peach [Prunus persica (L.) Batsch] caused by three be less effective when the disease is caused by P. cinnamomi. different Phytophthora species. Revista Mexicana de Fitopatología 23:33-41. Additional keywords: Soil matric potential, zoospores, soil- Abstract. In order to determine the influence of various water management. flooding episodes on the severity of root rot and crown rot of peach caused by Phytophthora spp., one-mo-old seedlings Resumen. Para determinar la influencia de varios períodos were grown for two months in potting mix artificially infested de inundación en la severidad de la pudrición de raíz (PR) y with P. cinnamomi, P. megasperma, or an unidentified del tallo al nivel del suelo (PTNS) causados por Phytophthora Phytophthora sp. (isolate SJ45). The soil matric potential spp. se utilizaron plántulas de durazno de un mes de edad, (ψm) was maintained constant at -20 millibars (mb) using las cuales se trasplantaron y cultivaron durante 2 meses en Büchner funnels as tension plates, or it was interrupted once sustrato para maceta infestado en forma artificial con P. every two weeks by flooding periods (ψm = 0) of 6, 12, 24, cinnamomi, P. megasperma o Phytophthora sp. (aislamiento or 48 h. At constant soil ψm = -20 mb, P. cinnamomi caused SJ45). El potencial mátrico del suelo (ψm) se mantuvo 48% root rot, but P. megasperma and the unidentified constante a -20 milibares (mb) usando embudos Büchner con Phytophthora sp. caused no measurable disease. P. platos de tensión o se interrumpió cada 2 semanas mediante megasperma caused virtually no disease when soil was períodos de saturación (ψm = 0) de 6, 12, 24 ó 48 h. A ψm = flooded (ψm = 0) for 6 or 12 h; however, it caused 62% root -20 mb constante, P. cinnamomi causó 48% de PR, en cambio rot and 0.7 crown rot index when the soil was flooded for 24 P. megasperma y Phytophthora sp. no causaron enfermedad. h, and 100% root rot and 2.8 crown rot index when the soil P. megasperma no causó enfermedad cuando el suelo se saturó was flooded for 48 h. The severity of the disease caused by (ψm = 0) durante 6 ó 12 h; sin embargo, causó 62% de PR y the unidentified Phytophthora sp. increased gradually as the un índice de 0.7 de PTNS cuando el suelo se saturó por 24 h flooding periods lengthened; it caused 36, 45, 74, and 100% y 100% PR y 2.8 de PTNS cuando el suelo se saturó por 48 root rot when the soil was flooded for 6, 12, 24, and 48 h, h. La severidad de la enfermedad causada por Phytophthora respectively, and caused crown rot only when 48 h floodings sp. se incrementó gradualmente de acuerdo a la prolongación were imposed. The respective root rot caused by P. cinnamomi de los períodos de saturación, causando 36, 45, 74 y 100% when seedlings were grown in soil flooded for 6, 12, 24, and de PR cuando el suelo se saturó por 6, 12, 24 y 48 h, 48 h was 55, 69, 91, and 100%. When peach leaf disks were respectivamente, mientras que la PTNS sólo ocurrió cuando used as bait for zoospores in flooded soil, the mean las plántulas se sometieron a saturación por 48h. Los percentages of disks infected by P. cinnamomi zoospores at porcentajes respectivos causados por P. cinnamomi cuando the baiting intervals of 0-2, 0-4, 20-24, and 44-48 h after las plantas se cultivaron en suelo inundado por 6, 12, 24 y 48 onset of flooding were 67, 78, 60, and 31%, respectively. At h fue de 55, 69, 91 y 100%. Cuando se utilizaron discos de these same baiting intervals, the incidence of disk infection hojas de durazno para el trampeo de zoosporas en el suelo by P. megasperma was 26, 68, 77, and 56%, and by the inundado, el porcentaje promedio de discos infectados por unidentified Phytophthora sp. was 23, 73, 98, and 95%. These P. cinnamomi en los intervalos de muestreo de 0-2, 0-4, 20- data suggest that careful soil-water management should 24 y 44-48 h después del inicio de la saturación del suelo 34 / Volumen 23, Número 1, 2005

fueron de 67, 78, 60 y 31%, respectivamente. En estos mismos In another study (Wilcox and Mircetich, 1985b), when the intervalos, la incidencia de infección en discos por P. rootstocks (Mahaleb and Mazzard cherry seedlings) were megasperma fue de 26, 68, 77 y 56%, y por Phytophthora grown in soil infested with P. cryptogea, root rot increased sp. fue de 23, 73, 98 y 95%. Los resultados sugieren que un as the duration of biweekly flooding periods increased from manejo cuidadoso del agua de riego puede reducir las 0 to 48 h; Mazzard was less susceptible than Mahaleb when pérdidas en árboles de durazno debido a PR y PTNS causado flooded for 24 h. The disease caused by P. megasperma in por Phytophthora sp. y P. megasperma, pero no sería efectivo both rootstocks was negligible when floodings were imposed cuando la enfermedad es causada por P. cinnamomi. for 0, 8, or 12 h; however, the disease was moderate and severe when soil was flooded for 24 and 48 h, respectively. Palabras clave adicionales: Potencial mátrico del suelo, Browne and Mircetich (1988), reported that P. cryptogea, P. zoosporas, manejo de agua en el suelo. cactorum, and P. cambivora, caused no root rot, 18% root rot and 60% root rot, respectively, in [Malus sylvestris The incidence of Phytophthora root and crown rot of peach (L.) Mill. var. domestica (Borkh.) Mansf.] when soil ψm was [Prunus persica (L.) Batsch] has increased over the last years maintained constantly at -20 mb. When different flooding in California’s commercial orchards, reaching epidemic periods were imposed, the disease increased with duration of proportions in some years (Mircetich, 1984). At the present flooding; when soil was flooded for 4 and 48 h, P. cryptogea time, sixteen different species of Phytophthora have been caused 10 and 52% root rot, respectively. P. cactorum, caused associated with peach trees in commercial orchards (Mircetich 13 and 46% root rot, and P. cambivora caused 80 and 89% and Browne, 1987). Pathogenicity tests have implicated P. root rot, respectively. In marginata Donn ex Sm., cactorum (Leb. and Cohn) Schroet., P. cambivora (Petri) there was no increase in infections by P. cinnamomi when 3 Buisman, P. citricola Sawada, P. cryptogea Pethyb. and Laff., to 4-month-old plants were waterlogged for a 4 day period P. drechsleri Tucker, P. megasperma Drechsler, P. before inoculation with zoospores. However, when plants citrophthora (R.E. Smith and E.H. Smith) Leonian, P. were waterlogged at the same time or after inoculation, there syringae (Kleb.) Kleb., P. cinnamomi Rands, P. parasitica was a significant increase in the severity of the disease Dast. and some unidentified Phytophthora spp. in root and (Davison and Tay, 1987). Flooding before inoculation did crown rot of peach in California (Mircetich, 1984; Mircetich not predispose Fraser fir [Abies freseri (Pursh) Poir.] to P. and Browne, 1987). This disease was called “wet feet” or cinnamomi; postflooding inoculation increased disease “sour sap” in the past because the highest incidence was dramatically (Kenerly et al., 1984). Sterne et al. (1977a), associated with wet and poorly drained soils (Day, 1953; reported that the percentage of avocado (Persea americana Smith, 1941). Soil water status has a great influence on the Mill.) roots infected by P. cinnamomi averaged varied from biology of Phytophthora spp. High soil moisture levels 80-90%, 50-90%, and 10-50% at soil matric potentials of 0, stimulate formation of sporangia and release (MacDonald -0.05, and -0.10 bar, respectively; only a few lesions occurred and Duniway, 1978a) and movement of zoospores (Duniway, at -0.25 bar. Observations by Mircetich and Keil (1970) 1976). It also stimulates direct germination of sporangia and indicated that decline and death of peach caused by P. survival structures like oospores and chlamydospores (Kuan cinnamomi in Maryland and Pennsylvania was common in and Erwin, 1982; Sterne, et al., 1977a; 1977b). Also, host poorly drained soils, but the disease also occurred in well- physiology can be altered by prolonged periods of soil drained soils. However, at the present time no detailed saturation, increasing susceptibility to Phytophthora spp. It information is available on the effect of soil water status on has been suggested for rhododendron (Rhododendron root and crown rot of peach caused by species of aberconwayi Cowan) (Blaker and MacDonald, 1981) and Phytophthora. Therefore, the objetives of this work were: a) (Medicago sativa L.) (Kuan and Erwin, 1980) that to study the influence of different lengths of flooding periods prolonged flooding periods caused disruption of root on root and crown rot of peach caused by thee Phytophthora membranes and exudation of substances that attracted species, and b) the relationship of severity of root and crown zoospores. The effect of flooding duration on the severity of rot and infectivity of zoospores of these pathogens. root and crown rot usually depends on the species of Phytophthora and the host. For example, P. cryptogea, P. MATERIALS AND METHODS megasperma, and P. drechsleri caused negligible root and Duration of soil flooding on disease severity. Phytophthora crown rot on Mahaleb cherry (Prunus mahaleb L.) when the cinnamomi (isolate 2-1-4) and P. megasperma (22-2-5) from soil was maintained at matric potential (ψm) of -10 or -25 peach and an unidentified species of Phytophthora (isolate millibar (mb) interrupted by 4 h of flooding (ψm = 0) once SJ45) recovered from surface irrigation water in San Joaquin every two weeks. In contrast, P. cambivora caused moderate Co., California, USA (Mircetich et al., 1985) were used in to severe disease at the same ψm values. When soil ψm was this study. Inocula was prepared as described previously maintained at -25 mb and flooded for a period of 48 h every (Mircetich and Matheron, 1976). Fungi were grown in two weeks, severe disease was caused in Mahaleb cherry by vermiculite-V8 broth contained in 0.5 L canning jars for 4-5 all four Phytophthora spp. (Wilcox and Mircetich, 1985a). weeks. The inoculum was washed with tap water using funnels Revista Mexicana de FITOPATOLOGIA/ 35 with two layers of cheesecloth until the excess of flooding combination. Because the results of the two unassimilated nutrients was eliminated. The inoculum was experiments were similar, detailed statistical analysis is added to UC potting mix (Baker, 1972) at the rate of 25 cm3 presented for only one. Before doing the analysis of variance, per L of potting mix. Two experiments were conducted in a a log10 transformation of the data from root and fresh shoot greenhouse where temperatures ranged from 20 to 33°C. weights was performed following procedures suggested by Incandescent light was provided to maintain a photoperiod Little and Hills (1973). A series of orthogonal contrasts were of 15 h. The soil matric potential (ψm) was controlled by made with the transformed data to determine the effect of the using Büchner funnel as tension plates as described in different flooding periods on the severity of disease caused previous reports (Duniway, 1975a; 1975b ; 1976). The potting by the Phytophthora spp. mix infested with Phytophthora spp. or the control consisting Trapping of zoospores in flooded soil. To determine the of UC potting mix and vermiculite not colonized by the relative activity of zoospores during the 48 h flooding periods, pathogens was packed in each Büchner funnel by adding 100- zoospore trapping was done at intervals of 0-2, 0-4, 20-24, 120 cm3 of potting mix and pressing the mix against the and 44-48 h after onset of every flooding placing an 89 ml tension plate and the wall of the funnel. When about two cup on the surface of the potting mix in the funnels. The thirds of each funnel was filled, one Lovell peach seedling, bottom of each cup had earlier been removed and replaced 30-day-old, trimmed to 16 cm high, was transplanted into with a nylon cloth having 20 µm openings that allowed the each funnel. Soil was added to a volume of 500 cm3 in each flood water to move into the trap cup, but prevented funnel. The seedlings were grown in 30 cm3 plastic cups with Phytophthora structures other than zoospores from entering. UC potting mix before transplanting into the funnels. After Ten 6-mm peach leaf disks from actively growing 2- to 3- the seedlings were transplanted to the Büchner funnels, 100 month-old peach seedlings were placed in the water which ml of distilled water was added to wet the soil and allow it to entered the trap cup from the flooded soil. The leaf disks drain to the predetermined ψm in the funnels. The soil matric were allowed to remain in the water for periods of 2 and 4 h potential (ψm) was adjusted to -20 mb using the midpoint of at each flooding interval. At the end of each baiting period, the soil column in the funnels as a reference point. The funnels the leaf disks were rinsed gently with tap water, removed and reservoirs were then wrapped with aluminum foil to avoid from the trap cup, blotted dry on a paper towel for a few growth of algae and to reduce evaporation. Distilled water seconds, then plated on PARP selective medium containing was added to the reservoirs when needed to maintain the water 10 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, column at the proper level; half-strength Hoagland’s solution and 100 mg of pentachloronitrobenzene (Kannwischer and was used the last 20 days of the experimental periods because Mitchell, 1978). The plates were incubated at 21°C for one the seedlings showed slight symptoms of nitrogen deficiency. weekk and the percentage of peach leaf disks from which To initiate the flooding treatments, the procedures as described Phytophthora colonies developed was determined. The previously (Browne and Mircetich, 1988) were followed; two baiting experiments were repeated eight times over the two weeks after transplanting the tubing system that connected experiments concerned with the effect of different flooding the Büchner funnels with the reservoir of Hoagland’s solution periods on disease severity. The data of all the replications was plugged, then the top of the soil was uncovered and were combined and processed in an analysis of variance and flooded with distilled water to the extent that 5-10 mm of a series of orthogonal contrasts to determine the relative water stood on the surface. The flooding treatments, which activity of zoospores of Phytophthora spp. in relation to the raised the soil ψm to 0 for periods of 0, 6, 12, 24, and 48 h, trapping intervals during 48 h flooding period. were imposed on seedlings inoculated with each of the thee Phytophthora spp. and the uninoculated controls. The RESULTS nonflooded seedlings were maintained constantly at ψm = - Influence of duration of flooding on disease severity. The 20 mb. At the end of the flooding treatment, the tubing system results of disease severity are summarized in Table 1 and was unplugged and the funnels allowed to drain to -20 mb, Figure 1. Highly significant (P < 0.01) differences among which required 10 to 15 min. After re-equilibrating, the tops Phytophthora spp. and flooding periods were detected. The of the funnels were covered again with aluminum foil. This Phytophthora sp. x flooding interaction was also highly flooding process was repeated every two weeks. The significant. The progressive reduction of root and shoot fresh experiment was repeated two times and the data were collected weights caused by flooding of Phytophthora-infested soil for within two months. At the end of the experiments, factors periods of 6 to 48 h was greater than the weight reductions used to assess disease severity were the root and shoot fresh seen in the corresponding flooding controls (Contrast 1, Table weights; furthermore, the percentage of root system rotted, 1). Nonflooded and flooded treatments were compared and and the proportion of crown rot were visually estimated. The then contrasted between the different Phytophthora spp. The extent of crown rot scale varied from 0 to 4 where 0 = no contrast between P. cinnamomi vs Phytophthora sp. (isolate crown rot, 1 = > 0 to 1/4 girdled, 2 = > 1/4 to 1/2 girdled, 3 = SJ45) and P. megasperma was highly significant (P < 0.01) > 1/2 to < completely girdled, and 4 = completely girdled. when the reduction of root and shoot fresh weight was There were 6 seedling replicates for each Phytophthora sp.- considered (Contrast 2), but it was not significant between 36 / Volumen 23, Número 1, 2005

Table 1. Analysis of variance of log10 root and fresh weight data from one of two experiments on the effect of duration of flooding on root and crown rot of peach (Prunus persica) caused by three Phytophthora spp. Root fresh weightw Shoot fresh weightw Source of variation df MS F MS F Block 2 0.0145 0.3825ns 0.0097 0.2635ns Inoculum 3 3.4651 91.4274**x 2.5989 70.6222** Flooding 4 2.9285 77.2691** 3.4159 92.8233** Flooding x inoculum 12 0.2459 6.4881** 0.3088 8.3777** Contrasts 1. Nonfloodedy vs floodedz x controls vs 1 7.2423 197.3378** 5.4298 141.7702** Phytophthora spp. 2. Nonflooded vs flooded x P. cinnamomi vs Phytophthora sp. and P. megasperma 1 3.0883 84.1498** 2.2154 57.8433** 3. Nonflooded vs flooded x Phytophthora sp. vs 1 0.0640 1.7438ns 0.0020 0.0522ns P. megasperma 4. Linear trend in flooded x control vs 1 1.3966 38.0544** 2.0437 53.3603** Phytophthora spp. 5. Linear trend in flooded x P. cinnamomi vs Phytophthora sp. and P. megasperma 1 0.5813 15.8392** 0.5415 14.1383** 6. Linear trend in flooded x Phytophthora sp. vs 1 0.1307 3.5613ns 0.1650 4.3080ns P. megasperma Error 84 0.0379 0.0368 w Root and shoot fresh weight values were multiplied by 10 before transformation to log10. xIndicates F values significant at P < 0.01; ns= not significant. yψm maintained constantly at -20 mb. zψm= -20 mb interrupted biweekly by flooding from 6-48 h.

Phytophthora sp. and P. megasperma (Contrast 3). A greater insignificant root rot when the soil was flooded for 6 and 12 reduction of root and shoot fresh weights was induced by P. h, but when the 24 and 48 h flooding periods were imposed, cinnamomi in soil maintained at ψm= -20 mb without flooding the mean root rot was 62 and 100%, respectively. Crown rot than by Phytophthora sp. and P. megasperma (Fig. 1 A and indices were less correlated with root fresh weight (r = -0.60) B). The linear trend component indicated that as the flooding than root rot (r = -0.84). Only P. cinnamomi caused crown periods were prolonged from 6 to 48 h, the reduction of root rot when seedlings were grown in soil maintained constantly and fresh weights was greater in seedlings grown in infested at ψm = -20 mb. In general, the mean crown rot scores soil than those in noninfested soil (Contrast 4). The linear increased as the flooding periods lengthened; indeces of 1.2, trend of reduction in root and shoot weight caused by P. 2.2, 1.7, 1.3, and 4 resulted when 0, 6, 12, 24, and 48 h cinnamomi, when compared to Phytophthora sp. and P. floodings were imposed. P. megasperma caused mean crown megasperma, was also highly significant (P < 0.01), (Contrast rot scores of 0.7 and 2.8 in seedlings flooded for 24 to 48 h, 5). The linear trend of Phytophthora sp., when compared respectively; it did not cause crown rot at shorter intervals of with P. megasperma, was not significantly different (Contrast flooding. Phytophthora sp. caused a mean crown rot score 6). The root fresh weight was inversely related to the percent of 4.0 when flooding interval of 48 h was imposed; no crown of root rot (r = -0.84). The root rot (Fig. 1C) in the rot was observed with shorter flooding episodes. noninoculated controls flooded for 0 to 48 h ranged from 2 Trapping of zoospores in flooded soil. When zoospore traps to 4%. P. cinnamomi caused 48% root rot when the soil was were placed close to seedlings in flooded soil, highly maintained at ψm= -20 mb without flooding; when soil was significant (P < 0.01) differences among replications (runs), flooded for 6, 12, 24, and 48 h root rot was 55, 69, 91, and intervals of baiting, and Phytophthora spp. were found. The 100%, respectively. Phytophthora sp. and P. megasperma run x Phytophthora sp. and intervals of baiting x caused negligible root rot at the same soil ψm; the respective Phytophthora sp. interactions were highly significant (P < mean root rot values were 55 and 68% when flooding periods 0.01), whereas the run x intervals of baiting interaction was of 6 and 12 h were imposed. The mean amount of root rot not significant (Table 2). When the data were subjected to a ranged from 91 to 100% when flooding periods of 24 and 48 series of orthogonal contrasts, the linear trends of the peach h were imposed. The root rot caused by Phytophthora sp. leaf disks infected by zoospores over the successive baiting increased progressively as the flooding periods lengthened intervals between Phytophthora sp. vs P. cinnamomi and P. from 6 to 48 h. In contrast, P. megasperma caused megasperma was highly significant (P < 0.01) (Contrast 1, Revista Mexicana de FITOPATOLOGIA/ 37

Control Phytophthora megasperma Phytophthora sp. Phytophthora cinnamomi 2.4 A 2.2 2

1.8 1.6

1.4 1.2

1 0.8

2.4 B 2.2 2 1.8 1.6 1.4 1.2 1 0.8

120 C 100

80

60

Root rot (%)40 Log 10 root fresh wt (g) Log 10 shoot fresh wt (g)

20

0 0 6 12 24 48 Hours of flooding Fig. 1. Effects of duration of flooding on: A, shoot fresh weight; B, root fresh weight; and C, percent of root rot of Lovell peach (Prunus persica) grown for 2 months in soil artificially infested with P. megasperma, Phytophthora sp. (isolate SJ45), P. cinnamomi or a noninfested control. Soil matric potential (ψm) was maintained at -20 mb except when floodings (ψm = 0) of 6, 12, 24 and 48 h were imposed once every two weeks. Data points are means of six replicates for each Phytophthora-flooding combination. 38 / Volumen 23, Número 1, 2005

Table 2. Analysis of variance of percent infections of peach (Prunus persica) leaf disks used as bait for zoospores of three Phytophthora spp., in two experiments about the effects of various soil flooding periods on disease severity. Source of variation df MS F Runy 7 15961.7 4.30**z Interval of baiting 3 7461.4 19.13** Phytophthora sp. 2 2277.2 5.84** Run x Phytophthora sp. 14 1095.0 2.81** Run x interval of baiting 21 625.5 1.60 ns

Interval of baiting x Phytophthora sp. 6 4686.2 12.02**

Contrasts 1. Linear trend over intervals of baiting x Phytophthora sp. vs P. cinnamomi and P. megasperma 1 15335.6 18.58** 2. Linear trend over intervals of baiting x P. cinnamomi and P. megasperma 1 7929.5 9.60** 3. Quadratic trend over intervals of baiting x Phytophthora sp. vs P. cinnamomi and P. megasperma 1 781.6 0.947ns 4. Quadratic trend over intervals of baiting x P. cinnamomi vs P. megasperma 1 1277.5 1.548ns Error 42 389.1 yA run = one replication in the baiting experiment. The baitings were conducted 8 times during the experimental periods. zIndicates F values significant at P < 0.01; ns = not significant.

Table 2). The same occurred when the linear trends between conditions of prolonged soil saturation. In the present study P. cinnamomi and P. megasperma were compared (Contrast it was found that different flooding periods had different 2, Table 2). The interaction of quadratic trend during the effects on the severity of disease depending on the species of intervals of baiting x Phytophthora sp. (isolate SJ45) vs P. Phytophthora. P. cinnamomi caused 48% root rot and cinnamomi and P. megasperma was not significant (Contrast considerable reduction of root and shoot fresh weights in soil 3, Table 2). The quadratic trend during the intervals of baiting maintained at ψm= -20 mb, but not flooded. Initially, the soil x P. cinnamomi vs P. megasperma was not significant either was infested with mycelium and numerous chlamydospores (Contrast 4, Table 2). The percent of leaf pieces infected by of P. cinnamomi and it seems likely that chlamydospores and zoospores of Phytophthora sp. and of P. megasperma was sporangia germinated directly at this matric potential and similar in the first two h of baiting (Fig. 2); the mean percent caused infections. This, in addition to the high susceptibility of baiting pieces infected was 23 and 26, respectively. Bait of Lovell peach, may have contribuited to a considerable infection by zoospores of Phytophthora sp. (isolate SJ45) development of the disease in peach seedlings at a ψm -20 increased over successive baiting intervals: 73, 99, and 95% mb. The results indicate that a ψm -20 mb permits germination of the peach leaf disks were infected in the baiting intervals of chlamydospores and sporangia of P. cinnamomi. In fact, of 0-4, 20-24, and 44-48 h after onset of flooding (Fig. 2). In lower matric potential values have been reported to stimulate the same baiting intervals, the percentages of bait infection germination of chlamydospores. Sterne et al. (1977a) found by P. megasperma zoospores were 68, 77, and 56%, that the chlamydospores of P. cinnamomi germinated at soil respectively. P. cinnamomi zoospores were the most active ψm from 0.0 to -0.25 bar. The same authors found that the during the first two h of flooding (mean infection of baiting percentage of diseased avocado roots caused by germinating pieces was 68%); their activity remained about the same in chlamydospores was moderate to severe when soil was 0-4 h baiting interval and declined gradually in the 20-24 maintained from -0.01 to 0.0 bar matric potential (Sterne et and 44-48 h baiting intervals to 60 and 31%, respectively al., 1977b). P. cinnamomi was found to produce the most (Fig. 2). sporangia at -160 mb, with upper and lower matric potential limits of about -10 mb and -2,500 mb, respectively (Gisi et DISCUSSION al., 1980). Our results support previous findings of Matheron The results presented here are consistent with previous and Mircetich (1985) and Kenerly et al. (1984) who found observations (Mircetich and Keil, 1970; Mircetich, 1984) that that P. cinnamomi caused severe disease of walnut [Juglans Phytophthora root and crown rot of peach is severe under hindsii (Jepson) Jepson ex R.E. Sm.] and Fraser fir in Revista Mexicana de FITOPATOLOGIA/ 39

Control Phytophthora megasperma Phytophthora sp. Phytophthora cinnamomi 120

100

80

60

40

Peach leaf disks infected (%) 20

0 0 - 2 0 - 4 20 - 24 44 - 48 Interval of baiting after flood initiation (h) Fig. 2. Percenf of peach (Prunus persica) leaf disks infected when used as bait for zoospores of Phytophthora megasperma, Phytophthora sp., P. cinnamomi and a noninfested control. Leaf disks remained in flooded soil at the intervals of 0-2, 0-4, 20- 24 and 44-48 h after flood initiation. The data points represented mean perfect of 8 runs where the leaf disks were exposed to infection by zoospores of the Phytophthora spp. unsaturated soil. Contrary to P. cinnamomi, P. megasperma seedlings to infection by zoospores and subsequent caused virtually no decay of roots when biweekly flooding development of the disease, as it has been reported in other periods of 0, 6, and 12 h were imposed. However, the disease Phytophthora - host combinations (Blaker and MacDonald, was moderate and severe when the soil was flooded for 24 1981; Kuan and Erwin, 1980; Stolzy et al., 1965). It seems and 48 h, respectively. Similar results were reported by Wilcox likely that sporangia were present in the soil infested with and Mircetich (1985) when Mahaleb and Mazzard cherry Phytophthora sp. (isolate SJ45) and P. megasperma and rootstocks were grown in soil infested with P. megasperma release of zoospores occurred in the first two h of flooding. and subjected to the same flooding periods. The disease Pfender et al. (1977) found that the maximum production of severity caused by the unidentified Phytophthora sp. (isolate sporangia by P. megasperma occurred in flooded soil, but SJ45) from irrigation water was clearly proportional to production took place also at - 0.05 and - 0.01 bar matric duration of the flooding periods. It behaved similarly to P. potential. They indicated that zoospore release began 6-8 h cryptogea when cherry (Wilcox and Mircetich, 1985), apple after onset of flooding. In the present study, zoospore activity (Browne and Mircetich, 1988), and walnut (Matheron and was detected in the first two h of flooding in soil previously Mircetich, 1985) were grown in infested soil that was maintained at ψm = -20 mb. These differences could be due subjected to various flooding periods. On the basis of to differences in methodology in the experiments. However, morphological characteristics, our unidentified species of our results are consistent with those of MacDonald and Phytophthora (isolate SJ45) fits in group VI of Waterhouse’s Duniway (1978a), who indicated that zoospore discharge keys (Waterhouse, 1963) where P. cryptogea is assigned. The occurred within 60 to 90 min in completely saturated soil release and dispersal of zoospores of the Phytophthora spp. (ψm = 0). Although some variation in the zoospore activity included in this study were enhanced by flooding conditions. of the Phytophthora spp. was detected over the baiting Zoospores of P. cinnamomi were the most active of the three intervals, it was evident that the activity persisted during the species in the first two h of flooding. This early and high 48 h of flooding. Such prolonged activity could be the result activity of the zoospores and the high susceptibility of peach of sporangia produced de novo after the onset of flooding to the pathogen could have contributed to the severity of the and subsequent release of zoospores, but this possibility was disease even without prolonged flooding periods. Activity of not investigated. MacDonald and Duniway (1978b) reported zoospores was detected during the first two h of flooding in that zoospores of P. megasperma appeared to lose motility Phytophthora sp. and P. megasperma, but a considerable quickly after release. Hickman (1970) on the other hand, severity of the disease, particularly by the latter, was indicated that depending on the species, zoospores remained manifested only after 24 and 48 h of flooding. Perhaps the motile for periods up to several days in the absence of soil prolonged flooding periods predisposed Lovell peach particles. The present study suggests that careful soil water 40 / Volumen 23, Número 1, 2005

management would minimize losses due to root and crown MacDonald, J.D., and Duniway, J.M. 1978a. Influence of rot of peach caused by P. megasperma and the unidentified the matric and osmotic components of water potential on species of Phytophthora, but such measure might not be zoospore discharge in Phytophthora. Phytopathology effective to control P. cinnamomi. 68:751-757. MacDonald, J.D., and Duniway, J.M. 1978b. Influence of LITERATURE CITED soil texture and temperature on the motility of Baker, K.F. 1972. The U.C. System for producing healthy Phytophthora cryptogea and P. megasperma zoospores. container grown plants. University of California, Division Phytopathology 68:1627-1630. of Agricultural Sciences. Agricultural Experiment Station Matheron, M.E., and Mircetich, S.M. 1985. Influence of Extension Service, No. 23. Berkeley, California, USA. 322 flooding duration on the development of Phytophthora root p. and crown rot of Juglands hindsii and Paradox walnut Blaker, N.S., and Mac Donald, J.D. 1981. Predisposing effects rootstocks. Phytopathology 75:973-976. of soil moisture extremes on the susceptibility of Mircetich, S.M. 1984. Phytophthora root and crown rot and rhododendron to Phytophthora root and crown rot. stem canker of peach trees. pp. 17-21. In: Proc. the 83rd. Phytopathology 71:831-834. National Peach Council Convention, Myrtle Beach, South Browne, G.T., and Mircetich, S.M. 1988. Effects of flood Carolina, February 18-23, 1984. duration on the development of Phytophthora root and Mircetich, S.M., and Browne, G.T. 1987. Phytophthora root crown rots of apple. Phytopathology 78:846-851. and crown rot of deciduous fruit trees: progress and Davison, E.M., and Tay, F.C.S. 1987 The effect of problems in etiology, epidemiology and control. pp. 64- waterlogging on infection of Eucalyptus marginata 95. In: N.E. Looney (ed.) . Proceedings of the Summerland seedlings by Phytophthora cinnamomi. New Phytologist Research Station. Commemorative Symposium: 105:585-594. Challenges and Opportunities in Fruit Production, Day, H.L. 1953. Rootstocks for stone fruits. California Protection and Utilization Research. The Summerland Agricultural. Experiment Station. Bulletin 736. Berkeley, Research Station, Agriculture Canada. Summerland, B.C., California, USA. 80 p. Canada. 132 p. Duniway, J.M. 1975a. Limiting influence of low water Mircetich, S.M., Browne, G.T., Krueger, W., and Scheader, potential on the formation of sporangia by Phytophthora W. 1985. Phytophthora spp. isolated from surface water- drechsleri in soil. Phytopathology 65:1089-1093. irrigation sources in California. Phytopathology 75:1346- Duniway, J.M. 1975b. Formation of sporangia by 1347. (Abstr). Phytophthora drechsleri in soil at high matric potentials. Mircetich, S.M., and Keil, H.L. 1970. Phytophthora Canadian Journal of Botany. 53:1270-1275. cinnamomi root rot and stem canker of peach trees. Duniway, J.M. 1976. Movement of zoospores of Phytopathology 60:1376-1382. Phytophthora cryptogea in soil of various textures and Mircetich, S.M., and Matheron, M.E. 1976. Phytophthora matric potentials. Phytopathology 66:877-882. root and crown rot of cherry trees. Phytopathology 66:549- Gisi, U., Zentmyer, G.A., and Klure, L.J. 1980. Production 558. of sporangia by Phytophthora cinnamomi and P. palmivora Pfender, W.F., Hine, R.B., and Stanghellini, M.E. 1977. in soils at different matric potentials. Phytopathology Production of sporangia and release of zoospores by 70:301-306. Phytophthora megasperma in soil. Phytopathology Hickman, C.J. 1970. Biology of Phytophthora zoospores. 67:657-663. Phytopathology 60:1128-1135. Smith, R.E. 1941. Diseases of fruits and nuts. California Kannwischer, M.E., and Mitchell, D.J. 1978. The influence Agricultural Extension Service Circular 120. Berkeley, of a fungicide on the epidemiology of black shank of California, USA. 167 p. tobacco. Phytopathology 68:1760-1765. Sterne, R.E., Zentmyer, G.A., and Kaufmann, M.R. 1977a. Kenerly, C.M., Papke, K., and Bruck, R.I. 1984. Effect of The effect of matric and osmotic potential of soil on flooding on development of Phytophthora root rot in Fraser Phytophthora root disease of Persea indica. fir seedlings. Phytopathology 74:401-404. Phytopathology 67:1491-1494. Kuan, T.L., and Erwin, D.C. 1980. Predisposition effects of Sterne, R.E., Zentmyer, G.A., and Kaufmann, M.R. 1977b. water saturation of soil on Phytophthora root rot of alfalfa. The influence of matric potential, soil texture and soil Phytopathology 70:981-986. amendment on root disease caused by Phytophthora Kuan, T.L., and Erwin, D.C. 1982. Effect of soil matric cinnamomi. Phytopathology 67:1495-1500. potential on Phytophthora root rot of alfalfa. Stolzy, L.H., Letey, J., Klotz, L.J., and Labanauskas, C.K. Phytopathology 72:543-548. 1965. Water and aeration as factors in root decay of Citrus Little, T.M., and Hills, F.J. 1973. Agricultural Experimentation sinensis. Phytopathology 55:270-275. Design and Analysis. John Wiley and Sons, New York, Waterhouse, G.M. 1963. Key to the species of Phytophthora USA. 350 p. de Bary. Mycolological Paper 92. Commonwealth Revista Mexicana de FITOPATOLOGIA/ 41

Mycological Institute, Kew, Surrey, UK. 22 p. Wilcox, W.F., and Mircetich, S.M. 1985b. Effects of flooding Wilcox, W.F., and Mircetich, S.M. 1985a. Influence of soil duration on the development of Phytophthora root and water matric potential on the development of Phytophthora crown rots of cherry. Phytopathology 75:1451-1455. root and crown rot of Mahaleb cherry. Phytopathology 75:648-653.