Comparative early growth of cotton seedlings expressing a visible true leaf at emergence and normal phenotype seedlings

Abstract

At emergence, a cotton seedling of a normal phenotype has a poorly developed first true leaf and a photosynthetic area essentially limited to the cotyledons. After emergence, the expansion of the first true leaf and the vegetative development is slow, lengthening the seedling stage, thus increasing vulnerability to biotic and abiotic stresses. Plants of several breeding lines were found to express a visible first true leaf at emergence (VTLE), which may be associated with rapid growth through the seedling stage. The objectives were to compare early growth of seedlings expressing a VTLE with that of seedlings of a normal phenotype, and to compare their growth when cotyledons were removed at different times after emergence. In the first test, plants were rogued for either a VTLE or normal phenotype, and sampled 10, 20 and 30 days after emergence (DAE). Plants with a VTLE had more nodes, photosynthetic area and plant dry weight than plants of a normal phenotype. In the second test, either one or both cotyledons were removed at emergence and at 5-day intervals between 5 and 20 DAE. Removal of both cotyledons was more detrimental than the removal of one. Plant growth increased as the time of cotyledon removal was delayed from emergence. Even with cotyledon removal, plants expressing a VTLE grew more than plants of a normal phenotype. Differences associated with the expression of a VTLE were more conspicuous early in the plant development.