Factors influencing the population dynamics of Meloidogyne konaensis on coffee in Hawaii

Abstract

Experiments were conducted in the greenhouse, field and growth chambers to evaluate effects of soil type, soil moisture regimes, and porosity on selected aspects of the dynamics of the Kona coffee root-knot nematode, Meloidogyne konaensis. First, the reproduction and damage potential of M. konaensis on resistant and susceptible rootstocks of coffee in four soils under two moisture regimes representative of areas where coffee is grown in Hawaii were assessed in greenhouse experiments. M. konaensis suppressed growth of coffee in all four soils. Nematode reproduction occurred readily in all soil types. Reproduction was lowest in the Hydric Dystrandept soil where the nematode holotype was found. In contrast, root galling was greatest in this soil. Greater galling occurred under constant moisture (33kPa) than under fluctuating moisture conditions in this soil. A field experiment in Kainaliu, Hawaii was conducted to determine the influence of irrigation, plant age, cultivar and nematode on coffee growth and yield. The population densities of the nematode in the soil varied according to plant age and irrigation treatment. Soil populations under irrigated conditions were greater during the months of May to July which normally follows the greatest annual precipitation and a period of active plant growth. Nematode reproduction was greater on coffee transplanted as 6-month-old seedlings than on coffee transplanted at 12- month ofage. Soil water tension varied by season and experimental treatment. Trees from 12-month-old transplants exhibited greater water tension fluctuation with greatest water tension occurring from January to April. Trees transplanted as 6-month-old seedlings into M. konaensis infested soil and irrigated yielded greater coffee fruit than the same aged trees treatment without irrigation. Crop loss and reduction of growth and yield were also more evident from 6-month-old seedlings without supplemental irrigation treatment. In contrast, yield from plots in treatments including irrigation, nematode and 12-month-old transplants yielded poorly. Overall highest yields were obtained from trees free of nematode and with supplemental irrigation. Yield reductions from nematode-infected plants ranged from 30-60% which is economically significant. Penetration, development and reproduction of M. Iwnaensis was determined on tomato as model plant at 0.77 and 0.65 porosity. The rate of root penetration and post-embryonic developmental rates occurred slightly faster the porosity treatment of 0.77 than in the more densely packed soil (porosity of 0.65). Development in the 0.65 porosity progressed slower than at 0.77. Even though the nematodes matured faster and began laying eggs sooner on plants growing at porosity of 0.77, much greater numbers of eggs were laid by 30 days after inoculation at the 0.65 porosity treatment than those at the 0.77 porosity. The finding from this research illustrates the primary role of the Kona coffee root-knot nematode in the Coffee Decline. The soil environment and host suitability are conducive factors for the coffee decline disease. Proper soil moisture management combined with sources of genetic resistance could minimize the damage enabling the coffee industry to remain profitable.