Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/12/2002
Publication Date: N/A
Interpretive Summary: There are many kinds of microscopic worms called nematodes that feed on the roots of cotton and other crops, debilitating the plants and markedly decreasing yields. The direct losses to U.S. cotton farmers caused by nematodes were estimated by the National Cotton Council in 1999 to exceed $300,000,000. The reniform nematode is one of the most important nematodes on cotton in the U.S. No cotton cultivars available to farmers are resistant to the reniform nematode but several kinds of wild cotton show a moderate level of reniform nematode resistance in pots. In this study, several of the most promising of these wild cottons were tested for the first time under field conditions in south Texas. However, the resistant wild cottons were not resistant in the field. Subsequent micro- plot and growth chamber studies revealed that the loss of resistance by these plants was unrelated to sunlight, outside temperatures, or the particular strain of nematode present. By the process of elimination, an unknown biological factor present in this soil but not in other soils tested appears responsible for the loss of nematode resistance by these plants. Understanding such factors will be essential to the successful incorporation of moderate levels of reniform nematode resistance into commercial varieties.
Technical Abstract: Greenhouse pot studies conducted previously by several laboratories identified certain primitive accessions of exotic cottons that show potential as sources of reniform nematode resistance for breeding programs aimed at developing reniform nematode resistant cultivars. In 2001, the first field experiment was conducted to directly examine the ability of the most promising of these accessions to reduce reniform nematode populations in the field. Statistically significant (P=0.05) nematode population suppression was achieved only for GB-264, and the level of suppression measured (48%) was not considered agronomically useful. Follow-up experiments conducted under microplot and growth chamber conditions confirmed that these accessions were able to exhibit moderate to high levels of resistance in a sandy loam soil and in a sand-based potting mix but not in soil taken directly from the Weslaco field site. Loss of resistance expression was unrelated to nematode genotype, moisture, nematode extraction technique, ambient temperature or light quality. Possible remaining explanations included downward movement of nematodes in the field, potent antagonists in the upper soil profile in the field, and abnormal root-growth in pot and microplot experiments.