Relationships between Root‐Knot Nematode Resistance and Plant Growth in Upland Cotton: Galling Index as a Criterion

Abstract

The southern root‐knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] is one of the most destructive pests in the Cotton Belt of the USA. The lack of an economical evaluation method for RKN resistance has hindered the development of resistant cultivars. This investigation was conducted to develop an improved RKN evaluation technique. Twelve genotypes including seven susceptible (S) lines, one moderately resistant (MR) line, three highly resistant (R) lines derived from ‘Auburn 623 RNR,’ and one F1 between DP 33B (S) and ‘Auburn 634 RNR’ (R) were evaluated in the greenhouse for plant growth, RKN egg reproduction, and root galling in Experiment 1. RKN egg reproduction was highly and positively correlated with galling index and both were highly and negatively correlated with plant growth characteristics including plant height, number of leaves, plant and root weight. Galling index was confirmed to be highly significantly and negatively correlated with plant height and fresh weight in Experiment 2 with 9 parents and their 36 F1 hybrids. Galling index had highest genotypic F value and comparable coefficient of variance (CV) to the plant characteristics, while CV for egg counts was very high. Correlation between the two greenhouse tests in the 9 parental lines as measured by galling index was highly significant. Comparison between F1 and their parents in egg reproduction and galling revealed that the RKN resistance is partially dominant. Using a common check and double inoculation in each pot, galling index is an easy, quick and reliable method for screening large numbers of cotton plants.