Screening of Luffa cylindrica Roem. for resistance against Tomato Leaf Curl New Delhi Virus, inheritance of resistance, and identification of SRAP markers linked to the single dominant resistance gene

Sponge gourd (Luffa cylindrica Roem.) is a popular cucurbitaceous vegetable on the Indian sub-continent. The crop is severely affected by Tomato Leaf Curl New Delhi Virus (ToLCNDV) a Geminivirus causing a yellow mosaic disease which results in 100% crop loss. Natural epiphytotic and challenge inoculation experiments revealed that DSG-6, an advanced inbred breeding line of L. cylindrica Roem., was resistant to ToLCNDV during both the Spring-Summer and rainy seasons of 2006 and 2007. Resistance was confirmed by PCR amplification with viral coat protein gene-specific primers that revealed a gene-specific band of 750 bp in susceptible (positive control) plants, but no 750 bp band in resistant plants. The inheritance of ToLCNDV resistance was studied through challenge inoculations in F-2 and backcross (B-1 and B-2) populations of a cross between a resistant female (DSG-6) and a susceptible male parent ('Pusa Sneha'). This revealed the dominant monogenic inheritance of the resistance gene. Two sequence-related amplified polymorphism (SRAP) markers were closely-linked to the ToLCNDV-susceptible gene in the susceptible parent and in a susceptible bulk population, while two SRAP markers were closely-linked to the resistance gene in the resistant parent and in a resistant bulk population. The SRAP markers thus identified can be used for early seedling selection in a large number of genotypes and should speed-up the development of Luffa cultivars that are resistant to ToLCNDV, thereby decreasing the incidence of this disease in this crop.