SPATIAL DISTRIBUTION OF MELOIDOGYNE SPECIES AND RACES IN THE TOMATO (LYCOPERSICON ESCULENTUM MILL.) PRODUCING REGION OF MORELOS, MEXICO R. A. Guzman-Plazola1*, J. de Dios Jaraba Navas1, E. Caswell-Chen2, E. Zavaleta-Mejía1, and I. Cid del Prado-Vera1 1Colegio de Postgraduados, Campus Montecillo, km 36.5 carretera México Texcoco, Estado de Méx- ico, C.P. 56230 and 2Departament of Plant Pathology and Nematology, University of California Davis, California 95616 USA. *Corresponding author: [email protected] ABSTRACT Guzman-Plazola, R. A., J. Jaraba N., E. Caswell-Chen, E. Zavaleta-Mejía, and I. Cid del Prado V. 2006. Spatial distribution of Meloidogyne species and races in the tomato (Lycopersicon esculentum Mill.) pro- ducing region of Morelos, Mexico. Nematropica 36:215-229. Regional spatial patterns of Meloidogyne species and races infecting tomato crops in Morelos state were analyzed from 50 tomato fields in the municipalities of Atlatlahucan, Tlayacapan, Totolapan and Yecapixtla. Rhizosphere soil was collected at each site and evaluated for soil texture, organic mat- ter content, pH and electrical conductivity. Soil collected at each site was distributed in five 2-liter plastic pots. Four tomato seedlings cv. Rio Grande were planted in each pot. Ten to 20 egg masses per positive site were extracted and individual egg masses were placed in the root zone of an individ- ual tomato plant of the same variety. Galling of each was assessed by the Taylor and Sasser Root Gall index. Fourteen out of fifty tomato fields contained Meloidogyne spp., but isolates from only eight fields were able to reproduce on tomato cv. Rio Grande. Thirty three isolates from all sites were iden- tified to species using morphological and morphometric parameters. Species and races from twenty one of those isolates found in the region were: Meloidogyne incognita race 1, M. arenaria race 2 and M. javanica race 1 based on North Carolina Differential Host Test. At the regional level, Meloidogyne spp. were found distributed in three areas. Soils positive for Meloidogyne were moderately to slightly acid, and most of them had 38 to 71% sand and 13 to 29% clay content Soil organic matter content and pH were highly correlated with principal components I and II, respectively. This correlation al- lowed us to classify soils from all the sampled sites into four groups of edaphic similarity. Conducive- ness of soils to Meloidogyne was assessed by means of a logistic regression model of Meloidogyne presence versus sand and clay content. Sand and clay content were useful to forecast the conducive- ness of Meloidogyne spp. in the tomato producing soils of Morelos. Key words: clay, Meloidogyne arenaria race 2, M. incognita race 1, M. javanica, regional spatial pattern, sand. RESUMEN Guzman-Plazola, R. A., J. Jaraba N., E. Caswell-Chen, E. Zavaleta-Mejía, y I. Cid del Prado V. 2006. Dis- tribución espacial de especies y razas de Meloidogyne en la zona productora de tomate (Lycopersicon esculentum Mill.) en Morelos, Mexico. Nematropica 36:215-229. Se analizó el patrón de distribución regional de las especies y razas de Meloidogyne asociadas al cul- tivo de tomate en el estado de Morelos, México. Se muestrearon cincuenta campos cultivados con tomate en los municipios de Atlatlahucan, Tlayacapan, Totolapan y Yecapixtla. De cada sitio se tomó una muestra de suelo rizosférico. En cada muestra se determinó la textura, el contenido de materia orgánica, el pH y la conductividad eléctrica. Estas variables se utilizaron para determinar, mediante regresión logística, cuáles características del suelo están asociadas a la ocurrencia de Meloidogyne en esa región. La muestra de suelo de cada sitio fue distribuida en cinco macetas de plástico de dos litros, donde se trasplantaron cuatro plántulas de tomate Río Grande. Se colectaron 10 a 20 masas de hue- vos por sitio positivo. Las masas fueron inoculadas por separado en tomate. Se evaluó el grado de aga- 215 216 NEMATROPICA Vol. 36, No. 2, 2006 llamiento mediante la escala de Taylor y Sasser. Las especies de Meloidogyne presentes fueron identificadas mediante variables morfológicas y morfométricas. Las razas se determinaron mediante la prueba de hospedantes diferenciales de Carolina del Norte. Se detectaron 14 sitios positivos para Meloidogyne, pero sólo de ocho se lograron incrementar las poblaciones de estos nematodos en toma- te cv. Río Grande. Se obtuvieron 33 aislamientos que se identificaron hasta especie. En 21 de éstos se determinaron las razas. Las especies y razas identificadas fueron: Meloidogyne incognita raza 1, M. are- naria raza 2 y M. javanica. Se observó que a nivel regional Meloidogyne spp. se distribuye en tres áreas claramente identificadas. Los suelos positivos para Meloidogyne tuvieron un pH moderadamente a li- geramente ácido, porcentajes medios a altos de arena y bajos contenidos de limo y arcilla. El conte- nido de materia orgánica y el pH se encontraron altamente correlacionados con el componente principal I y II, respectivamente, lo que permitió agrupar los suelos en cuatro grupos de similaridad edafológica. Sin embargo, solamente los contenidos de arena y arcilla resultaron variables útiles para pronosticar la presencia o ausencia de poblaciones de Meloidogyne en la zona productora de tomate del estado de Morelos, México. Palabras clave: arena, arcilla, Meloidogyne arenaria raza 2, M. incognita raza 1, M. javanica, patrón espa- cial regional. INTRODUCTION Nematodes cause an average of 21% yield loss in tomato crops worldwide Morelos is the eighth largest tomato (Sasser and Freckman, 1987). Ninety per- (Lycopersicon esculentum Mill.) producing cent of yield losses due to nematodes are state in Mexico. Tomatoes in this state are caused by root-knot nematodes (Agrios, mainly produced under non-irrigated rain- 1997). Few reports are available on nema- fall-dependent fields. Average tomato yield todes in tomato crops of Morelos State. In in Morelos is 20.4 ton/ha which is 17.2 and 1970, Palacios analyzed one tomato crop 27 ton/ha less than the average yield of in each of the 22 municipalities reported Sinaloa and Baja California, respectively as tomato producers at that time. He (SIAP-SIACON, 2004), the largest tomato found Meloidogyne incognita and M. arenaria producing states in Mexico. Low produc- in all sampling sites. Pacheco (1986) and tivity of tomato crops in Morelos is caused Cid del Prado et al. (2001) reported by poor soil fertility, irregular rainfall, M. incognita race 1 in Tenextepango, inappropriate crop management practices, municipality of Ayala. However, tomatoes and the incidence of pests and diseases. are no longer produced in fields sampled Virus diseases are the most important, but in these three reports. fungi and nematodes (Meloidogyne spp. and According to interviews with tomato Nacobbus aberrans Thorne and Allen) may growers from Morelos, nematicides are cause important yield losses (Flores, 1997). applied in a preventative manner. Growers In 1985, 6187 ha were cultivated with routinely apply nematicides to the soil tomatoes, but by 2001 this area was along with other chemicals to control soil reduced to only 2830 ha (SIAP-SIACON, pathogens. Generally, no technical criteria 2004). Moreover, only six out of 21 munici- are followed. The identification of species palities originally reported as tomato pro- and races of root-knot nematodes attack- ducers in 1980 continued to produce ing tomato crops in the region, along with tomatoes in 1999 (Atlatlahucan, Tepoztlán, an analysis of their spatial distribution, and Tlalnepantla, Tlayacapan, Totolapan and an assessment of nematode incidence and Yecapixtla) (INEGI, 1999). potential damage, would allow advisers Distribution of Meloidogyne on tomato in Mexico: Guzman-Plazola et al. 217 and growers to assess both the current and planted into each pot. Three months later potential economic importance of nema- all plant roots were examined for the pres- todes. Such information would serve as ence of galls and ten to twenty egg masses decision support criteria for the applica- were collected from each positive plant. tion of management strategies. The analysis of spatial distribution of Inoculum Production nematodes has mostly been focused on sin- Ten to 20 egg masses were collected gle fields. At this scale, plant-parasitic nem- from each field. Single egg masses of atodes are typically distributed in clusters Meloidogyne spp. were placed close to the (Barker, 1985). Aggregation of nematode roots of individual tomato seedlings cv. Rio populations is considered to be a conse- Grande. A mixture (1:1:1) of autoclave quence of their strategy of reproduction sterilized sand, organic soil, and perlite and their dispersal mechanisms. Few stud- (Agrolite, Dicalite de Mexico, S.A.) was ies on regional distribution of nematodes used as a growth substrate. have been carried out; however, this type of analysis may help explain the role of Isolate and Site Characterization these organisms in agricultural systems. In this research, species and races of root- Ninety days after the last inoculation knot nematodes (Meloidogyne spp.) associ- cycle roots from infected plants were col- ated with tomato crops in Morelos and lected and new egg masses were extracted. their regional distribution and relation- Females were stained using sodium ships to soil factors were analyzed. hypochlorite-acid fuchsin technique (Daykin and Hussey, 1985). Second-stage juveniles (J ) were collected by hatching eggs at room MATERIALS AND METHODS 2 temperature. Males were extracted from Soil Sampling and Root-knot Nematode Detection rhizosphere soil by wet sieving and centrifu- gation (Hooper, 1986). Males and juveniles Fifty tomato fields in the tomato grow- were fixed, dehydrated and mounted in glyc- ing region of Morelos were sampled. erin. Seinhorst’s Massive Dehydration Tech- Twenty seven tomato fields were sampled nique modified by Bongers (personal in the municipality of Totolapan, nine in communication) was followed: Nematodes Yecapixtla, eight in Tlayacapan and six in were killed by heating the suspensions to Atlatlahucan (Fig. 1). Fields to be sampled approximately 40°C before fixing them in were selected arbitrarily.