Development of improvedCitrusrootstocks through hybridization

Abstract

Citrus rootstocks have pronounced effect on scion vigour and size, yield, fruit size and juice quality. Citrus rootstock improvement is challenging because so many traits are to be packaged into a single successful rootstock. Rough lemon (Citrus jambhiri Lush.) is the most commonly used rootstock for Nagpur mandarin (Citrus reticulata Blanco), but it is susceptible to Phytophthora (root and foot rot) diseases and citrus nematode. To combine the vigour and high yielding qualities of rough lemon with the resistance of trifoliate orange (Poncirus trifoliata L.) and Troyer citrange (Citrus sinensis x Poncirus trifoliata) for Phytophthora and citrus nematode, a hybridization programme was carried out during 1990–91 and 1991–92. The hybrid seedlings were evaluated for vegetative and reproductive characteristics up to 2005–06. Segregation for different characteristics was observed in the F1 itself. For a rootstock to be successful, it should have faster growth in the nursery and the hybrids 2.6 (rough lemon x Troyer citrange) and 3.1 (rough lemon x trifoliate orange) were vigorously growing in the nursery. Bud take was quite good in all the rootstock hybrids. The hybrids so developed (2.6 and 3.1) will broaden the genetic base of our citrus industry once they are tested for biotic and abiotic stress tolerance/resistance. Further, the hybrids 2.6 and 3.1 are similar to rough lemon in all aspects and have very few trifoliate leaves (0.01%). They are performing well in the field and nursery and their growth is at par with rough lemon. In the development of these hybrids, the germplasm of trifoliate orange and Troyer citrange would play an important role in future breeding programmes for the improvement of citrus rootstocks. The hybrids developed are further being screened for their tolerance/resistance to Phytophthora spp. and citrus nematode and they are also being evaluated for testing the performance of Nagpur mandarin budded on them.