Variability in ‘Rough Lemon’ × ‘Sour Orange’ Hybrids for Foliar Traits and their In vitro Screening against Phytophthora nicotianae

Phytophthora nicotianae, a deadly fungus, causes huge damage to citrus. Developing tolerant rootstocks is an eco-friendly solution to manage it. In this study, we characterized 21 ‘Jatti khatti’ (a strain of ‘Rough lemon’) × ‘Sour orange’ hybrids for four leaf traits and determined their tolerance against Phytophthora nicotianae using in vitro leaf inoculation method. For leaf traits, the hybrids displayed a higher magnitude of variation than the parents. The hybrids represented five different leaf lamina shapes, six leaf apex types, three leaf margins and three petiole wing shapes. The appearance of novel leaf variability pointed to the possibility of recombination in parental gametes. In leaf inoculation based screening, the susceptibility to Phytophthora infection was related to the size of lesions on leaf discs. The parents ‘Jatti khatti’ and ‘Sour orange’ recorded significantly different sized lesions of 2.6 and 1.3 cm, respectively. The hybrid 83-3 produced significantly smaller lesion size (1.0 cm) while six other hybrids recorded lesions of size similar to ‘Sour orange’. Hence, these seven hybrids can be considered tolerant to Phytophthora and can be further tested for other biotic and abiotic stresses to ultimately find a rootstock that possess most of the desirable features of the two parents.