JIA-2019-11

2501 NIE Jun-jun et al. Journal of Integrative Agriculture 2019, 18(11): 2492–2504 The boll weight of J169 was the largest, followed by L21 and 99B during the five-year period. The boll number per plant was not consistent among the three cultivars from 2013–2017. In addition, the lint percentage of the Bt cotton varieties was only slightly increased in different periods. These conclusions suggest that the increase in lint yield was primarily due to the increase in large bolls, a suggestion that is consistent with previous studies (Mao 2010; Iqbal et al . 2013; Shakeel et al . 2015). 4.1. Effects of plant-type difference on yield formation Plant type is the spatial arrangement and combination of morphological and functional attributes of all of the organs that affect the characteristics of light transmittance and the spatial distribution of bolls (Feng et al . 2016). In our study, J169 had much looser plant architecture and greater plant height than L21 and 99B; these properties were helpful in increasing the size of the vegetative organs and optimizing the light environment and consequently, promoting boll- setting and large boll formation. However, in the rainy year, this variety was more likely to overgrow, which led to the closed and poor light conditions that induced fruit-shedding from the lower and middle sympodial branches, similar to J169, which had the lowest number of middle bolls in the wet year (2013, rainfall was 591.7 mm during the cotton growing season). In contrast, the tight architecture of 99B, and especially L21, was slightly affected by the rainy conditions. 4.2. Contribution of within-plant distribution bolls to lint yield In addition to the influence of genetic characteristics, cotton yield and fiber quality are also affected by the spatial positions of bolls (Dong et al . 2014; Mao et al . 2015; Chen et al . 2016). In the previous studies, the fruit of the first node on the same sympodial branch contributed more to yield than the others (Jenkins et al . 1990; Heitholt et al . 1993; Liu et al . 2015). Wu et al . (2018) reported that the seedcotton weight of the first node in the first to third fruiting branches was the least affected by the light and temperature. The main reason of cotton yield reduction was that the number and weight of bolls at third fruiting branch decreased under late planting and shading (Zhao et al . 2018). The results of the current study indicated that the spatial variation of bolls differed significantly among the three varieties. Jiman 169 had the highest number of inner bolls and the largest boll weight with the loosest plant architecture; L21 had the highest number of bolls in the lower and middle positions and the second largest bolls with the tightest plant architecture; and 99B had the lowest number of bolls per plant, the highest number of distal bolls, and the smallest individual boll weight. Hofs et al . (2006) reported that a higher number of internal bolls Table 6 Fiber quality across different boll-weight of Bacillus thuringensis (Bt) cotton varieties in 2013–2017 Year 1) Variety 2) Fiber length (mm) Fiber strength (cN tex –1 ) Micronaire Fiber uniformity (%) Fiber elongation (%) 2013 J169 28.11±0.36 b 29.40±0.29 b 4.95±0.05 a 83.14±0.16 a 4.80±0.11 b L21 29.79±0.35 a 31.65±0.55 a 4.60±0.17 b 84.85±0.39 a 5.04±0.11 ab 99B 28.27±0.42 b 32.92±0.34 a 4.62±0.05 b 83.98±0.33 a 5.17±0.01 a 2014 J169 29.45±0.45 b 29.51±0.05 b 4.76±0.14 a 84.68±0.15 a 6.79±0.05 b L21 31.14±0.13 a 32.14±0.29 a 4.00±0.09 c 85.64±0.56 a 7.13±0.08 ab 99B 29.93±0.26 b 32.41±0.52 a 4.41±0.16 b 85.29±0.22 a 7.27±0.13 a 2015 J169 29.63±0.49 b 29.63±0.32 b 4.72±0.12 a 84.67±0.15 a 6.76±0.10 b L21 31.33±0.25 a 32.22±0.33 a 3.78±0.04 c 85.28±0.61 a 7.06±0.01 ab 99B 29.73±0.07 b 32.04±0.47 a 4.37±0.15 b 85.21±0.31 a 7.19±0.09 a 2016 J169 29.00±0.07 b 28.59±0.42 b 4.88±0.10 a 85.26±0.47 a 6.64±0.03 a L21 30.58±0.41 a 31.54±0.79 a 4.22±0.03 b 86.37±0.22 a 6.79±0.05 a 99B 29.73±0.29 ab 30.97±0.55 a 4.78±0.05 a 86.24±0.16 a 6.78±0.02 a 2017 J169 28.27±0.04 a 27.53±0.21 c 5.68±0.06 a 84.08±0.45 a 6.57±0.00 a L21 29.63±0.28 a 29.25±0.38 b 5.12±0.02 b 84.57±0.08 a 6.67±0.02 a 99B 28.59±0.37 a 30.93±0.41 a 5.41±0.11 a 84.83±0.79 a 6.67±0.04 a CV (%) J169 2.36 b 3.05 b 7.88 c 0.95 a 13.45 a L21 2.52 a 3.88 a 12.23 a 0.82 b 13.11 a 99B 2.60 a 2.77 c 8.94 b 0.96 a 12.83 a P -value Y 0 0 0 0 0 V 0 0 0 0 0 Y×V 0.5902 0.0030 0.1857 0.2387 0.0006 1) CV, coefficient of variation. 2) J169, Jimian 169; L21, Lumianyan 21; 99B, Daizimian 99B. Y and V mean year and variety, respectively. Values are mean±standard deviation. Values followed by a different small letter within same row are significantly different in a column at 0.05 probability level.