Sowing date and boll position affected boll weight, fiber quality and fiber physiological parameters in two cotton (Gossypium Hirsutum L.) cultivars

To study the effects of sowing date and boll position on fiber quality and the physiological mechanism, field experiments were conducted using two cotton cultivars (Kemian 1 and Sumian 15) with two sowing dates (normal sowing date 25 April, and late sowing date 25 May) at Nanjing (118°50′E, 32°02′N), Jiangsu, China, in 2006 and 2007. Cotton bolls were divided into three parts (low, middle and upper) according to the fruiting branch symbodial positions. Boll weight, fiber quality (bundle strength, span lengths, micronaire), and fiber physiological parameters (cellulose content, callose content, and sucrose transformation rate) were detected, respectively. Boll weight and fiber strength were affected by sowing date, boll position, and sowing date × boll position. Comparing to the normal sowing date, late sowing date declined boll weight, fiber strength, cellulose content, and sucrose transformation rate. The cellulose content and sucrose transformation rate changed with boll position, and consequently resulted in the change of boll weight and fiber strength. In normal sowing date, cotton boll in middle positional sympodial branch had the highest cellulose content, sucrose transformation rate, boll weight, and fiber strength. In late sowing date, cotton boll in low positional sympodial branch had the highest cellulose content, boll weight and fiber quality. The results indicated that the change of fiber yield and quality in sowing dates and boll positions were because the synthesis of cellulose, callose and sucrose were changed. Increasing the cellulose content and sucrose transformation rate can improve yield and fiber quality in late sowing date or sub-optimal environmental conditions.