Backcrossing of intergeneric hybrid (C. papaya x V. avercifolia) with IPB papaya inbred lines in two population sites in the Philippines

In the backcrossing of intergeneric hybrid (C. papaya x V. quercifolia) wth IPB papaya inbred lines two pollination sites in the Philippines were established. These were in Mainit, Bay, Laguna [Philippines], an area with high PRSV disease pressure and Davao National Crop Research and Development Center Bago- Oshiro, Davao City [Philippines], a totally PRSV-free region. The objectives of this paper are to compare the performance of five inbred lines (3878, 4172, 4108, 5648 and 5893) based on their ability to produce fruits, seeds and viable embryos under two environments. Second, determine the number of male flowers of intergeneric hybrid line 410 that will increase embryo yield. And lastly, to evaluate the PRSV resistance of different intergeneric hybrids (410, 404, 468, 469, and 507) under heavily PRSV infected field. All four inbred lines (3878, 4108, 4172 and 5648) planted in Davao when crossed to line 410 produced varying number of fruits, seeds and embryos. In a PRSV-free environment the amount of seeds and embryos developed were not positively correlated with the number of fruits successfully pollinated. In contrast, from the five inbred lines (3878, 4108, 4172, 5648 and 5893) used in Mainit, Bay, Laguna, line 3878 consistently failed to set fruits when pollinated with line 410. The rest of the inbred lines produced varying number of fruits, seeds and embryos. Based on the cross done in two sites, 4108 x 410 consistently showed the highest percentage of fruits harvested with viable embryos. The female to male ratio in pollination was increased from 1:10 to 1:20 on the four crosses (4108 x 410 x 4172 x 410 x, 5648 x 410 and 5893 x 410). Results of 1:20 showed that crosses 4172 x 410 and 5648 x 410 significantly increased the number of seeds produced but not the number of embryos. However, 5893 x 410 significantly increased the number of viable embryos generated. Under a heavily PRSV infected field, intergenetic hybrid lines 410 and 468 remained virus-free. PRSV symptoms were observed on intergeneric hybrids 404, 469 and 507. This was further confirmed by the ELISA test results.