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.

Reproduction of root knot nematode (</i>Meloidogyne incognita<i>) on Bt cotton expressing Cry1Ac and Cry2Ab2 protein

“…M. incognita lays about 300-400 eggs and it completes its lifecycle in 33-38 days (Banu, 2007). Galling index in cotton is a measurement of its response to infection by M. incognita and it is correlated to yield reduction in susceptible cultivars (Zhang et al, 2006). Large values of egg mass and galling index had a negative effect on plant height number of squares/bolls, plant, shoot and root weight across all treatment.…”

BRS 368RF: A glyphosate tolerant, midseason upland cotton cultivar for Northeast and North Brazilian cerrado

“…For bacterial blight, resistance was confirmed by using SNP marker ); e Amaral disease index calculated (Amaral 1969) -data from two trials artificially inoculated with Colletotrichum gossypii var. cephalosporioides, by using methods proposed by Oliveira et al (2010); f Galling index (Zhang et al 2006); g Disease index (Machado et al 2009). …”

BRS 369RF and BRS 370RF: Glyphosate tolerant, high-yielding upland cotton cultivars for central Brazilian savanna

“…cephalosporioides, using the methods proposed by Oliveira et al (2010). Root-knot nematode galling index was measured using the methods described by Zhang et al (2006). Fusarium index was assessed as described by Machado et al (2009).…”

“…(Amaral 1969) -data from two assays artificially inoculated with Colletotrichum gossypii var. cephalosporioides using methods proposed by Oliveira et al (2010); e Galling index (Zhang et al 2006); f Disease index (Machado et al 2009); g Cotton cultivar IAC 25 was used as a resistant/partial resistant control.…”