Growth, yield and phenology of 2 hybrid papayas (Carica papaya L.) as influenced by method of water application

Highly variable, outcrossed papaya lines irrigated with overhead sprinklers were grown at Yarwun (151.3 degrees E, 23.75 degrees S) in Queensland, Aus tralia. The inherent variability made scientifically based comparative stud ies impractical. The advent of uniform hybrid papaya lines allowed the test ing of 2 of these hybrids under 3 irrigation methods, 2 of which had the po tential to greatly reduce water use compared with overhead sprinklers. Yiel ds of 92 t/ha.year were achieved by both papaya Hybrids 29 and 1E. Water ap plication method did not influence yield. About 26% of plants were lost due to the phytoplasma diseases dieback, yellow crinkle and mosaic over the li fe of the trial. Downward yield fluctuations were related to poor fruit set in winter when pollinators (Family Sphingidae) were not present and growth was slow due to hot dry periods affecting fruit set. The resultant fruit ( about 6 months later) were small and reduced in number. Irrigation with overhead sprinklers using saline water (1400-4000 mu S/cm) damaged leaves and reduced growth of plants. Winter spot was most severe in July, August and September, in Hybrid 29 with overhead irrigation. Height of plants 13 weeks after planting was greater under trickle irrigati on due to less damage from the saline water supply than in the overhead spr inkler treatment. Hybrid 29 set fruit at 94.3 cm above ground compared with 117.6 cm for Hybrid 1E.