Title: Effects of Meloidogyne incognita on the Yield and Quality of Sweet Potato in the Humid Lowlands of Papua New Guinea
Abstract: Field experiments were conducted in 2012 and 2013 to study the effects of inoculum densities of Meloidogyne incognita applied at 10, 100, 1000, 5000, and 10000 juveniles/eggs per 500 cm3 along with un-inoculated control treatments, on a susceptible sweetpotato variety, K9. At the highest initial inoculum (Pi), an average marketable tuber yield of 991 kg ha-1 was recorded compared to 3495.5 kg ha-1 from un-inoculated control, accounting for 72% relative yield reduction. Significant (p≤0.05) yield reduction of 37% was also recorded from the lowest Pi of 10 juveniles/500 cm3. Probit analysis projected that 50% loss to marketable tubers are likely to occur at populations as low as 40 nematodes/500 cm3.There was a high positive correlation (r = 0.87**) between percentage relative yield loss and initial inoculum densities. There was significant (p≤0.01) impairment in marketable tuber quality with 4% cracking at 10 M. incognita per 500cm3, increasing to 37% at the highest Pi of 10,000. Highly significant positive correlations were also observed for cracked tubers (r = 0.93**) and non-marketable tubers (r = 0.96**), when tested against the Pi densities of M. incognita. Nematode population was monitored during the cropping season revealed an overall significant increase (p≤0.05) in juvenile populations at mid-season (60 days after inoculation) from the initial inoculum populations. A reverse in trend of juvenile numbers was observed at harvest (120DAI).