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High susceptibility of many commercial clones of Para rubber tree (Hevea brasiliensis) makes disease management very difficult warranting development and use of disease tolerant clones. Hence, hybridization was carried out using high-yielding and susceptible clones of H. brasiliensis viz. RRII 105, RRII 414 and RRII 430 and two disease tolerant species viz. H. spruceana and H. camargoana and two wild Rondônia germplasm accessions viz. RO 380 and RO 2871. The progenies from the breeding are under various stages of evaluation for their growth and rubber yield. During the course of evaluation, it was observed that many progenies were affected by a serious leaf disease in the form of spots which affected only mature leaves. In all leaf samples examined, conidiomata and ascomata were observed from the initial stages of leaf spot symptoms. Based on characteristic morphology of conidiomata and ascomata, the fungus which was consistently detected in the spots was identified as Phyllosticta capitalensis. Occurrence of P. capitalensis in both of its conidiomata and ascomata states with appendaged conidia and appendaged ascospores respectively, in association with the characteristic leaf spots in either H. brasiliensis or its inter-specific hybrids, is a novel report from India or elsewhere. In very few progenies, leaf blight associated with Pestalotiopsis sp., was also observed. In order to find variability in response to the leaf spot disease associated with P. capitalensis, all progenies were assessed for disease incidence and severity. Progenies of crosses viz. RRII 430 x RO 2871, RRII 414 x H. spruceana, RRII 414 x RO 380 and RRII 105 x H. spruceana had more than 80 percent disease incidences in their progenies. Progenies of cross RRII 430 x RO 380 showed minimum disease incidence (I = 61%). Half-sib progenies of a disease tolerant clone Fx 516 showed lesser disease incidences (I = 25-27%) and very low disease index (DI, 0.8-0.9) indicating better tolerance. In addition to the above, few other high-yielding commercial rubber clones were assessed for their susceptibility to P. capitalensis associated leaf spot. In an on-farm trial, two clones viz. RRII 430 and RRII 417 recorded maximum (I = 60%) disease incidence. Clone RRII 422 (I = 10%) followed by RRII 414 (I = 20%) showed minimum disease incidence. Two other clones viz. RRII 105 and RRII 429 showed moderate incidence (I = 50%). P. capitalensis was consistently detected and associated in all of the infected leaf samples from all the host species observed from early stages of disease development. However, more detailed studies are required to ascertain its specific role in disease development in order to develop suitable management strategies. Plant Pathology & Quarantine 10(1): 100–110 (2020) ISSN 2229-2217 www.ppqjournal.org Article Doi 10.5943/ppq/10/1/12

plant pathology and quarantine journal of fungal biology

Variation in susceptibility to Phyllosticta capitalensis-associated leaf disease among inter-specific hybrids, half-sibs and high-yielding clones of Para rubber tree (Hevea)