Light attenuation within a row of crops such as cotton is influenced by canopy architecture, which is defined by size, shape and orientation of shoot components. Level of light interception causes an array of morpho-anatomical, physiological and biochemical changes. Physiological determinants of growth include light interception, light use efficiency, dry matter accumulation, duration of growth and dry matter partitioning. Maximum light utilization in cotton production can be attained by adopting cultural practices that yields optimum plant populations as they affect canopy arrangement by modifying the plant canopy components. This paper highlights the extent to which spatial arrangement and density affect light interception in cotton crops. The cotton crop branches tend to grow into the inter-row space to avoid shade. The modification of canopy components suggests a shade avoidance and competition for light. Maximum leaf area index is obtained especially at flowering stage with higher populations which depicts better yields in cotton production.
Cotton is a very important crop that consists of traits with different associationship due to genetic and environmental factors. In order to determine the degree of association between seed cotton yield and important traits, a study was done using an RCBD experiment with ten genotypes. Seed cotton yield, GOT, lint yield, boll weight, bolls per plant, seed weight, plant height, fibre length, elongation, fineness and strength data were collected and analysed. Genotypic and phenotypic correlation analysis was done in Meta R. Estimation of direct and indirect effects was done using path analysis in Microsoft Excel. Analysis of variance revealed significant differences for boll weight, seed weight, GOT and plant height. Seed cotton yield was correlated with lint yield (r = 0.71***), fibre elongation (r = 0.54***), bolls per plant (0.27***), seed weight (r = 0.22***), strength (r = 0.21***) and fineness (r = 0.13*) at genotypic level. Ginning outturn was correlated with lint yield (r = 0.70***), elongation (r = 0.60***) and strength (r = 0.50***). Boll weight was correlated with seed weight (r = 0.56***) whilst plant height was highly associated with fibre strength (r = 0.58***). The adjusted R Square (0.98), low standard error (0.12) and low residual effect (R = 0.01) in regression analysis indicated that ABOUT THE AUTHOR Chapepa Blessing is a plant breeder working at Cotton Research Institute of Zimbabwe as a cotton breeder. His research areas are developing, implementation analyzing data and information dissemination of the national cotton breeding program in the Department of Research and Specialist Services of the Ministry of Agriculture in the country. Other research interests include crop modelling using remote sensing technology and molecular tool applications. Marco Mare is also plant breeder at Cotton Research Institute and is involved in developing, implementation analyzing data and information dissemination of the national cotton breeding program. Washington Mubvekeri is the head of Cotton Research Institute and is responsible for all cotton research programs in the country.
BackgroundThe Zimbabwean national cotton breeding programme has the mandate to develop superior cotton (Gossypium Hirsutum) varieties with good field performance and high fibre properties. Cotton productivity in Zimbabwe has remained very low, with national average seed cotton yield record of 650kg ha-1 (AMA Report, 2019) compared to the potential 2000kg ha-1. Since this is a result of many biotic and abiotic factors, field experiments laid in a Randomized Complete Block Design were conducted on ten genotypes (seven test genotypes and three check varieties) from 2012 to 2019 across 13 diverse locations in Zimbabwe to evaluate cotton yield performance, stability and adaptability by Analysis of Variance (ANOVA) and Genotype and Genotype by Environment Interaction (GGE) Biplot methods. ResultsThe Analysis of Variance indicated significant (P< 0.001) effects of Genotype (G), Environment (E) and their Interaction (GE). The highest percentage of variation was explained by E/G/GE (60.34%) while G/E+GE together explained the rest of the variation (<40%). Joint effects of G and GE were partitioned using the GGE biplot analysis explaining total of 59.08% (PC1 = 36.96% and PC2 =22.12%) of the GGE sum of squares. The biplot analysis revealed that candidates 917-05-7, TN96-05-9, 912-05-1 and GN 96 (b)-05-8 were the ideal and stable genotypes. The candidate variety 917-05-7 significantly (P< 0.001) showed superior yield performance over checks CRI-MS1 and CRI-MS2 recording 5% and 5.5% yield increase respectively. Candidate 917-05-7 recorded a higher earliness index (78.11%) over checks CRI-MS1 and CRI-MS2 (77 and 76% respectively) thus indicating potential attributes for good cotton production with more pick-able bolls earlier than the current commercial varieties.ConclusionCandidate 917-05-7 has been identified as the ideal genotype in terms of high yielding potential, and stability hence recommended for commercial release and use as breeding parent for future breeding programs.
Verticillium wilt disease causes significant losses to cotton yield and varietal development for resistance is critical in combating this threat. A study was carried out to determine the underlying genetic pattern controlling disease resistance and identify suitable parental lines to use in varietal tolerance development. Five cotton varieties were crossed in a half diallel mating system to produce ten crosses and five selfed parental lines which were screened against Verticillium wilt by artificial inoculation. There were significant variations on the severity scores, vascular brown index scores, morphological and agronomical traits under Verticillium wilt pressure. The Verticillium wilt severity scores ranged from 1.22 to 3.07 and Vascular Brown Index scores from 0.78 to 2.77. The mean squares of general combining ability (GCA) for the various characteristics of the parents were significant and also for the specific combining ability (SCA) of the vascular brown index score which was 0.27 was also significant. Three parental lines were identified as breeding material with good GCA, morphological and agronomical performance and these were CRI-MS-1, SZ9314 and BC853. This study implies that varietal tolerance can be developed by incorporating genotypes with resistance genes in breeding programmes. Future work should focus on developing resistant varieties suitable for production in Verticillium wilt prone areas.
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