The existence of negative correlations, coupled with significant genotype x environment interaction (GE) among cotton traits poses both opportunities and challenges in breeding. This study aimed at determining the existence of GE on seed cotton (Gossypium hirsutum L.) yield, lint yield, earliness index, gin out turn ratio, 100 seed weight, split boll weight and fuzz grade and correlations, among these traits, as well as understanding the implications on variety evaluation and release. Ten genotypes from Cotton Research Institute, Zimbabwe, were evaluated across seven locations, during the 2012/13 and 2013/14 cropping years with three replications at each location. Seed cotton and lint yield, earliness index, gin out turn ratio, 100-seed weight, split boll weight and fuzz grade were measured on the genotypes at all locations. Analysis of variance for GE showed significant differences (P<0.05) on most traits, except earliness index. There were huge GE and error variance components on seed cotton yield and allied traits that reduced heritability and correlation among these traits. Seed cotton and lint yield were significantly correlated (P<0.001; r = 0.95) to each other; while split boll weight had significant correlation (P<0.004; r = 0.82) with 100-seed weight. The genotype plus GE biplot analysis showed that SZ 9523 had high and stable yield and desirable fuzz grade, which made it an ideal genotype for release. All locations belonged to one complex mega-environment with Chisumbanje Research Station more representative and most discriminating location which can be used in early generation testing of cotton.
The migration of Ug99 variants of Puccinia graminis f. sp. tritici is of concern to global wheat production (1). Seven races have been characterized in the Ug99 lineage (3), three of which occur in South Africa (4). During surveys of wheat fields for Ug99 in Zimbabwe and Mozambique in August and September 2010, high stem rust severities were found at Chiredzi, Chisumbanje, and Birchenough in Zimbabwe and at Rotanda in Mozambique. Stem rust was widespread in the lowlands (<800 m above sea level) of Zimbabwe and trace amounts were present in the mid-altitude areas. In Mozambique, stem rust was only observed at Rotanda (sample Moz1001). Collections from Chiredzi (samples Zim1004 and Zim1005), Chisumbanje (Zim1006), and Birchenough (Zim1009 and Zim1010) yielded viable urediniospores for infection studies. According to race analysis conducted on seedlings of the North American stem rust differential set (2) in a greenhouse at 18 to 25°C, Zim1005 and Zim1006 were typed as PTKST and Zim1004 and Zim1009 as TTKSF. Both TTKSF and PTKST were detected in the Zim1010 sample. Race analysis experiments were conducted three times. Urediniospores of isolate Moz1001 were not viable in infection studies, but yielded fungal DNA for simple sequence repeat (SSR) analysis. Using eight selected SSR primer combinations (4), all six isolates clustered within the Ug99 lineage. Isolates Zim1005, Zim1006, Zim1009, Zim1010, and Moz1001 and the stem rust control races TTKSF, TTKSK, and PTKST grouped into two main clusters, with Zim1009 and Zim1010 clustering together and sharing 88% similarity with the rest of the isolates. Zim1005 and Zim1006 were identical to TTKSF and TTKSK, respectively. Zim1004 shared 96% genetic similarity with the TTKSP control, with these two sharing 74% genetic similarity with the remaining isolates. The SSR data correlated with the infection data, except for Zim1004, which was typed as TTKSF but clustered close to TTKSP. Wheat cvs. SC Nduna, SC Shine, SC Stallion, SC Smart, Kana, Insiza, and Dande are predominant in Zimbabwe. Cv. SC Stallion and other unidentified cultivars were susceptible to P. graminis f. sp. tritici in the field in Zimbabwe. In Mozambique, the tall, local cv. Sitsonko was susceptible to P. graminis f. sp. tritici but no infections were observed on SC Nduna or SC Shine. The similarity in P. graminis f. sp. tritici races in Zimbabwe, South Africa, and Mozambique suggests that inoculum is exchanged within the region and explains the detection of race PTKST in South Africa in 2009. Trajectory models showed winds originating at Birchenough in October 2009, where stem rust was observed, passing directly over KwaZulu-Natal, South Africa within 48 to 72 h. Race PTKST was confirmed from collections in KwaZulu-Natal in November 2009 (4). The confirmation of Sr31 virulence in race PTKST in Zimbabwe is important because it provides new geographical records for an Ug99-related race and puts Southern African cultivars with 1B.1R resistance at risk. References: (1) D. Hodson. Euphytica 179:93, 2011. (2) Y. Jin et al. Plant Dis. 92:923, 2008. (3) R. F. Park et al. Euphytica 179:109, 2011. (4) B. Visser et al. Euphytica 179:119, 2011.
Ten (10) medium staple cotton genotypes comprising of five commercial varieties and five experimental lines were evaluated for field performance, genetic and environmental variability. The trials were laid out in a randomized complete block design (RCBD) with three replications. Analysis of variance was done for total seed cotton yield, lint yield, boll weight, earliness and gin out turn (GOT %) using Genstat 14 th edition while stability and adaptability analysis was done using the AMMI model and the GGE biplot software. Significant differences (P<0.05) in genotype performances were observed in all the traits except for boll weight and earliness. The environment (E) effect was significant (P<0.05) for seed cotton yield and gin out-turn percentage (GOT %). The genotype (G) effect significantly (P<0.05) accounted for differences in boll weight and earliness index. The genetic x environment (GEI) interaction was not significant across the two seasons. SZ 9314 showed wide adaptation to all environments, a well-known and recommended characteristic of the commercial variety. These results show that 644-98-11, 917-05-7 and SZ-95-7 are promising genotypes that can be registered for production in upland cotton ecologies worldwide and they can be incorporated in future cotton improvement program. It is suggested that fibre quality traits for these experimental lines should be assessed.
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