A cala 1517 cotton (Gossypium hirsutum L.) cultivars developed and released by the New Mexico Agricultural Experiment Station have historically had superior fi ber quality among commercial upland cotton cultivars (Smith et al., 1999; Zhang et al., 2005a,b). Although approximately 96% of the cotton hectarage in the United States is used to grow transgenic cotton cultivars (USDA-AMS, 2010), it is crucial that conventional elite cotton germplasm lines with high yield and good fi ber-quality potential continue to be developed to provide the necessary germplasm base for transgenic breeding. Furthermore, high-yielding, nontransgenic cotton cultivars with improved fi ber quality are needed for conventional cotton production or areas where
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.
The southern root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood) RKN] is one of the most destructive pests in the Cotton Belt of the U.S. Developing and employing resistant cultivars is the most economical and efficient method for RKN management. This greenhouse investigation was conducted to understand the quantitative genetic basis of RKN resistance in the major RKN resistance sources using a nine-parent diallel analysis based on improved RKN evaluation techniques. The selected genotypes consisted of three ÔAubrun 623 RNRÕ (here RNR ¼ Root-knot Nematode Resistance)-derived resistant lines, one moderately resistant cultivar ÔAcala Nem-XÕ, and five susceptible cultivars. Comparison between F 1 and their parents in galling index revealed that the RKN resistance is partially dominant. The general combining ability was more important than the specific combining ability for RKN resistance. The estimates for broad-sense and narrow-sense heritabilities on galling index were 0.82 and 0.65, respectively, indicating that RKN resistance in the Auburn and Nem-X resistance sources is largely controlled by genetic and additive effects. The minimum number of genes for RKN resistance was estimated to be two. Therefore, under reliable and uniform RKN inoculation and infestation conditions, single plant selection should be efficient in transferring Auburn RKN resistance into elite genetic backgrounds.The southern root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood)] race 3 is one of the major threats to US cotton production (Blasingame and Patel 2005). Developing and using resistant cultivars represents one of the most efficient and economical strategies in RKN management. In cotton, many moderately RKN resistant germplasms have been identified and a highly RKN resistant germplasm line, ÔAubrun 623 RNRÕ (here RNR ¼ Root-knot Nematode Resistance), was released by combining moderate resistance from both of its parents (ÔClevewilt 6Õ and ÔWild Mexico Jack JonesÕ) (Shepherd 1974c). A significant research effort has since been made to investigate the genetics and mechanisms of this resistance and to develop RKN resistant cultivars (McPherson et al. 1995, Colyer et al. 2000. The high level of RKN resistance from ÔAubrun 623 RNRÕ was transferred into various genetic backgrounds to develop a series of new RKN resistant lines, such as ÔAuburn 634 RNRÕ (in ÔAuburn 56Õ background) (Shepherd, 1982), M-240 RNR, and M-315 RNR (both in DP61 background) (Shepherd et al. 1996). The resistance from ÔClevewilt 6Õ was also used to develop the moderately resistant cultivars ÔLA 434 RKRÕ, ÔST LA 887Õ, and ÔPM 1560Õ. A moderately RKN resistant cotton cultivar ÔAcala Nem-XÕ was released with its resistance source unknown (Ogallo et al. 1999, Robinson et al. 1999). However, the high-RKN resistance level from the Auburn source has never been transferred into any commercial cotton cultivar.The inheritance of RKN resistance in ÔAubrun 623 RNRÕ and its derived resistant lines has been investigated since the 19...
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