Preliminary screening of citrus hybrids for identifying tolerance to Phytophthora nicotianae

Abstract

Phytophthora is one of the most devastating pathogens affecting citrus production. Breeding resistant genotypes is a durable strategy to manage this pathogen. In this study, in vitro screening of 31 citrus hybrids was done against Phytophthora nicotianae using detached leaf assay. The hybrids tested were developed in twoway crosses between Rangpur lime (RL, Phytophthora sensitive) and sour orange (SO, Phytophthora tolerant). The relative Phytophthora sensitivity was determined from the necrotic lesion area after three days of pathogen inoculation. The parents and hybrids could be differentiated into five resistance classes on the basis of necrotic lesion size and area. Among the 18 SO × RL (SR) hybrids, three hybrids viz. SR 3, SR 10 and SR 19 exhibited the least leaf necrotic length (2.8-3.7 mm), breadth (3.2-3.9 mm) and area (9.2-15.0 mm2), indicating a highly resistant reaction. From the 13 RL × SO (RS) hybrids, RS 6 and RS 22 showed highly resistant reaction by virtue of the least necrotic area (12.7-17.9 mm2). Twelve SR and four RS hybrids produced necrotic lesions of >216.8 mm2 area and were rated as highly susceptible in this assay. The parents- Rangpur lime and sour orange recorded highly susceptible and resistant reaction, respectively, which authenticated the results of the leaf assay. The five highly resistant hybrids identified in this study after ex vitro validation of Phytophthora tolerance should prove helpful in commercial citriculture.