THE BURROWING NEMATODE OF BANANA: STRATEGIES FOR CONTROLLING THE UNCONTROLLABLE

Abstract

The burrowing nematode of banana, Radopholus similis, is difficult, if not impossible, to control effectively. The lack of resistance in commercially acceptable cultivars and the perennial nature of the crop limit management options. Multiplecycle treatment with systemic nematocides is presently the only effective tool available for reducing damage and sustaining yield. Most of these compounds are not toxic to the burrowing nematode, but only inhibit nematode activity for short periods of time. The repetitive application of non-fumigant nematocides has led to an increase in the rapidity of their biodegradation. From environmental, toxicological and consumer viewpoints, this type of pest management is unacceptable. Many attempts have been made to improve the situation with little or no impact to date. Many nematocides have been or are being removed from the market, and new replacement compounds have not been developed. Resistance has never been detected in commercial banana cultivars, and genetically modified cultivars are still unacceptable to a large number of banana consumers. Microbialbased strategies are considered to be a promising alternative approach to nematode management in banana. Progress can only be made if research and crop production systems are streamlined to support new management concepts. The following are discussed: 1) biological enhancement of planting material with fungal endophytes; 2) treatments with multiple nematode antagonists with diverse modes of action; 3) importance of induced systemic resistance in biological control systems; and 4) use of molecular tools to detect effective antagonists. INTRODUCTION There are a large number of effective plant protection technologies available for the management of plant-parasitic nematodes. However, most, if not all, are not adaptable to commercial production systems and less so to subsistence banana and plantain farming. Most people are not aware that Radopholus similis is not controlled by nematocides currently used to secure yield and prevent toppling of the banana plant. Nematocides do not kill nematodes. The majority of systemic nematocides only inhibit movement of R. similis for 2 to 5 weeks. Therefore, nematocides only ensure healthy root growth for a short period. Nematocides are either biodegraded, diluted by rainfall or washed out of the rhizosphere shortly after their application. In addition, microbially enhanced biodegradation of nematocides increases with repeated applications over time (Ou et al., 1994; Karpouzas and Walker, 2000; Pattison et al., 2000; Moens et al., 2004). Microbial degradation also leads to increases in the number of nematocide applications/year, which aggravates the overall situation and disturbs the biological balance in the soil. More importantly, most of the nematocides presently being used are highly toxic to almost all organisms having a nervous system. Most banana crops are grown with nematocides that, for environmental and toxicological reasons, should not be on the market. If R. similis is to be managed without nematocides, new and effective management tools, that actually achieve control without environmental side effects, are needed. Proc. IS on Banana Crop Prot., Sust. Prod.