**6. Sources of resistance**

Plants that may be less desirable in other ways, but carry a useful disease resistance trait. Ancient known plant varieties and wild species, cultivated varieties and land races are very important to preserve because they are the most common sources of enhanced plant disease resistance. Source of resistance are available for melon aphid, striped and spotted cucumber beetles, squash bug, squash borer, pickleworm, red pumpkin beetle, fruit fly in different cucurbits, cabbage maggot

and aphid in cabbage and spinach, fruit and shoot borer in brinjal, jassids in okra, potato leaf hopper, melon fly in different beans, pea aphid and weevil. Genetic basis of insect resistance has been reported to be monogenically dominant in muskmelon aphid and in pumpkin and watermelon for fruit fly, whereas, additive gene action have been reported for resistance to both striped and spotted cucumber beetles and squash bug in squash. In interspecific crosses of muskmelon with wild melon two pairs of complimentary genes are reported to be involved for resistance to fruit fly. Maternal influence has also been indicated in inter-varietal crosses of squash for resistance to spotted cucumber beetle.

In India work on resistance of cucurbits to red pumpkin beetle and fruit fly was initiated at IARI, New Delhi as early during 1962 and at Indian Institute of Horticultural Research, Bangalore during 1969. A highly resistant source to fruit fly was obtained in pumpkin, which was utilized, in breeding a resistant variety Arka Suryamukhi. Some of the pumpkin lines were fairly resistant to red pumpkin beetle. It was observed that among the different species *Citrullus colocynthis* was highly damaged by fruit fly. In *Lycopersicon* genus *L.hirsutum* and *L. hirsutum f. glabratum* is resistant to fruitworm, and also indicated that since these were crosscompatible with *L. esculentum* and it was possible to transfer the resistance factor in the cultivated varieties. It was further indicated that *L. hirsutum f. glabratum* was also resistant to tobacco flea beetle and carmine spider mite. It was possible to incorporate resistance to more than one insect species in one genotype.

In Onion sources of resistance were identified, cause and mechanism studied and suitable varieties were developed. In Okra difference in varietal response to jassid attack was observed and fruit of the resistant line was found to have strong prickly hairs and was highly susceptible yellow vein mosaic virus. In spinach variety Manchuria was reported as resistant to aphid as early as in 1920. In Carrot resistance to fruit fly was reported and one of the amaranthus lines was observed to have high field resistance to grasshopper in Nigeria. With monogenic inheritance available for melon aphid in cantaloupe, for fruit fly in pumpkin and in watermelon it would be possible to utilize backcross method for incorporating resistant gene in commercial varieties.
