Aecidium Mori)

Indian Phytopath. 66 (2) : 144-149 (2013) RESEARCH ARTICLE Evaluation of resistance mechanisms of mulberry cultivars through component analysis of aecial infection cycle of mulberry red rust (Aecidium mori) ANGELINA T. GONZALES1* and OSCAR S. OPINA2 1DMMMSU-Sericulture Research and Development Institute, Banotan, La Union, Philippines 2Plant Pathology Department, University of the Philippines-Los Banos, Laguna, Philippines ABSTRACT: Component analysis of resistance showed that the resistant reaction conferred by resistant cultivars was attributed to its ability to limit or suppress sporulation capacity, prolong latent period and shorten the infectious period of the fungus. The cohort life statistics revealed that the survival rate, proportion of infection units of Aecidium mori Barclay at various infection states and infection efficiency of mulberry red rust (MRR) did not vary significantly among resistant (Alfonso), moderately resistant (S-13 and SRDC-2) and susceptible (M-local, S-54, S-61 and Batac) mulberry cultivars. Regardless of cultivar, high mortality of infection units was recorded during the early stages of infection process. Sporulation capacity, infectious period and latent period of A. mori significantly differed among resistant, moderately resistant and susceptible cultivars. The infectious period of A. mori on susceptible cultivars was longer (20-32 days) compared to moderately resistant (12-28 days) and resistant (10 days) cultivars. A. mori produced abundant aeciospores in susceptible cultivars, few to less abundant in moderately resistant cultivars and very few in resistant cultivar. The latent period is longer in resistant cultivar compared with susceptible cultivars. The observed resistant reaction cv. Alfonso can be attributed to its ability to limit or suppress sporulation capacity, prolong latent period and shortened infectious period of the fungus. Key words: Aecial infection cycle, Aecidium mori, component analysis, infectious period; latent period; sporulation capacity Mulberry, which belongs to the genus Morus of the family MATERIALS AND METHODS Moraceae, is widely distributed in Asia, Europe, North and Mulberry cultivars from India (S-13, SRDC-2, S-61, M-local South America and Africa, and is cultivated extensively in and S-54 (Almojuela et. al., 2005)), and two local varieties East, Central and South Asia for silk production (Awasthi (Alfonso and Batac) with different reactions to mulberry red et al., 2004). It is extensively grown as food plant for rust were used in the experiment. Cultivars S-61, M-local, S- silkworm, Bombyx mori L. and occurrence of mulberry 54 and Batac were rated as susceptible (S); cv. S-13 and diseases is among the major limiting factors affecting cocoon SRDC-2 were moderately resistant (MR) and cv. Alfonso was production. The most destructive disease appeared to be rated as resistant (R). Cuttings were prepared from mature the mulberry red rust (MRR) caused by Aecidium mori mulberry plants and were grown in sterilized soil. Each cultivar Barclay (Teotia and Sen, 1994; Govindaiah et al., 1992; was replicated 3 times. All recommended cultural practices Subrata and Biswas, 1992). It significantly decreases the were followed like fertilization, watering etc. to give favorable amount of moisture, crude protein, reducing sugars and total conditions for the vigorous growth and development of the sugars of the infected leaves and causes 10-30% leaf test plants. The methods of Opina and Valencia (1994) were yield loss and also decreases the nutritive value of leaves, adopted in conducting the experiment. hastens yellowing, senescence, and defoliation (Biswas et. al., 1994). Inoculum preparation and inoculation technique In the Philippines, MRR disease not only attack Heavily infected mulberry leaves showing symptoms of MRR established mulberry garden but also mulberry nurseries were collected from the field. Aeciospores were extracted (Kobayashi and De Guzman, 1988; Dizon, 1995). If MRR from infected plants using a spore collector connected to a continue to develop unabated, silk production can be vacuum pump (Fig. 1a). With the aid of improvised plastic seriously affected. So far, no related study has been settling tower, the spores were inoculated to the 3-month- conducted to investigate the resistance mechanisms of old mulberry saplings late in the afternoon. The inoculation mulberry cultivars against mulberry red rust caused by A. was done violently releasing approximately 1.0 gram of aeciospores on top of the settling tower. The tower provided mori, thus we used cohort life and reproductivity table an even distribution of aeciospores deposition on the leaves statistics to compare the interactions of A. mori and seven and also served as an incubation chamber for the inoculated mulberry cultivars in this study. plants. After 24 hours of incubation, the saplings were transferred from the settling tower to the greenhouse for *Corresponding author: [email protected] disease development. Indian Phytopathology 66 (2) : 144-149 (2013) 145 Fig.1. Inoculation preparation and aeciospore production: (a) spore collector attached to a vacuum pump; (b) active rust pustules Fig. 2. Different states of infection cycle of Aecidium mori observed releasing aeciospores (LPO); (c) germination process (40x); under the compound microscope: (a) aeciospores; (b) (d) pustule formation (10x); (e) early symptoms of MRR, 8-10 aeciospores with germtube; (c) aeciospores with distinct days after inoculation; and (f) advanced symptoms of MRR appressorium; (d) young and intact pustules; and (e-f) top view with eruptive pinhead lesions under surface of the leaves of mature pustules with aeciospores Data gathered and analysis States of MRR infection The life table statistics, reproductive table and area under The aeciospores of A. mori on the leaves of seven mulberry the sporulation progress curve (AUSPC) of A. mori on seven varieties were studied as they undergo infection process. The mulberry cultivars were constructed. different states of infection cycle were monitored under a compound microscope based on observable ungerminated Life table statistics aeciospores, germinated aeciospores, germtube formation, appressorium formation and pustule formation. The densities The life table statistics of MRR were determined for each cultivar. The mortality (q ) and survival (1-q ) ratios, proportion of infection units passing through the identified infection 1 1 of surviving infection units (l ) and survivorship curves of A. states were assessed at 3-day interval. These were the total 1 mori were established in the seven mulberry varieties. aeciospores density (TAD), germinated aeciospores density (GAD), germtube density (PUD) and surviving pustule density Reproductive table (SPD). The reproductive table was estimated based on the Measurement of infection units aeciospores produced, 10 to 14 days after inoculation at 2 day-interval. Ten days after inoculation, aeciospores After inoculation, leaflets of each cultivar were randomly production on plants was determined. Leaflets with known selected and detached at different time intervals. Leaf number of rust pustules were tagged and aeciospores were samples were carefully cut into pieces and were fixed in collected using a spore collector attached to a vacuum pump. formalin-aceto-alcohol combination (FAA) for 24 hours. Leaf The collected aeciospores were suspended in 1.0 ml distilled samples were decolorized for 24 – 48 hours in a Carnoy’s water with a drop of Tween 40 to ensure even dispersion of solution and stained in an acid-fuchsin staining solution for aeciospores. The density of aeciospores was determined 24 hours. The stained leaf samples were mounted on slides using a haemacytometer (Tuite, 1969). The measurements and were observed under a compound microscope. The of aeciospores production were taken at 2-day interval unit pustules have stopped sporulation in three replications. number of ungerminated aeciospores, germinated aeciospores, germtube appressoria (Low Power Objective RESULTS AND DISCUSSION (LPO magnification)) and pustules per 0.25 cm2 of leaf surface were determined. The measurements of infection units were The fate of the cohorts of infection units (aeciospores) as done in three replicates. they passed the different infection states on seven mulberry 146 Indian Phytopathology 66 (2) : 144-149 (2013) Table 1. Number of infection units of Aecidium mori per Low Power Objective (LPO) magnification of a compound microscope at different age intervals and state of infection process on seven mulberry cultivars Age interval Infection Resistant Moderately resistant Susceptible Average (days) state2 Alfonso S-13 SRDC-2 M-local Batac S-54 S-61 0 TAD 11.20 14.34 10.36 9.86 15.32 15.22 13.00 12.75 1 GAD 8.60 5.55 9.74 7.44 10.21 14.68 11.55 9.68 2 GTD 8.23 5.23 7.78 6.52 10.17 11.52 9.62 8.44 3 APD 2.98 4.07 4.55 3.86 5.21 7.47 3.83 4.56 9 PUD3 1.75 1.58 2.60 1.42 2.08 2.19 1.50 1.87 44 SPD 1Each figure is an average of infection units per low power objective (LPO) magnification 2TAD – total aeciospores density; GAD- germinated aeciospores density; GTD – germtube density; APD – appressorium density; PUD – pustule unit density; SPD – sporulating pustule density 3Each figure is an average of rust pustule in .25 mm2 leaf surface. Fig. 3. Proportion of surviving individual of Aecidium mori on the leaves of mulberry cultivars cultivars is shown in table 1. Out of an average of 12.75 Survival ratios aeciospores per microscopic field (LPO) deposited

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