Biological Control of Root-Knot Nematodes (Meloidogyne enterolobii) in Guava by the Fungus Trichoderma harzianum

Abstract

In Thailand, Nakhon Pathom, Samut Sakhon, and Ratchaburi provinces, which are in the central region of the country, are the largest areas for guava cultivation. Kimju and Pansithong are the most extensively grown cultivars, and they have been seriously damaged by two species of root-knot nematodes, Meloidogyne incognita and M. enterolobii (or M. mayaguensis). The latter species was only recently reported in Thailand but is common in China, Brazil, and the United States. Substantial numbers of guava trees are in decline and show reduced fruit production. In this survey study of six guava orchards in central Thailand, we found that common aboveground symptoms of nematode infection included yellowing, stunting, folded leaves, blighted and wilted leaves (especially when water was lacking), and slow ripening of fruits. Underground symptoms included root galls, partially rotted roots, and, in some cases, prolific production of adventitious roots to compensate for damaged and nonfunctional roots. When we examined the morphometric characteristics of second-stage juveniles of M. incognita and M. enterolobii obtained from soil around guava plants, we observed no significant correlation between the characteristics of the two species or between the characteristics of populations within each species (P>0.05). For the biological control of root-knot nematodes in guava, we evaluated a commercially available fungal agent, Trichoderma harzianum, which effectively controls several other soil-borne pathogens and has been shown to induce disease resistance and stimulate adventitious root growth in plants. We found that inoculation of the root zones of guava plants with T. harzianum reduced the number of nematodes in both soil and roots as compared to the number in untreated plants (P<0.05). Moreover, inoculation of guava plants with T. harzianum arrested the development of the juvenile nematodes (P<0.05). Trichoderma harzianum is less expensive than chemical control agents and poses no risk to the environment.