Effect of Mechanical Stress on Cotton Growth and Development

Citation: Zhang Z, Zhang X, Wang S, Xin W, Tang J, et al. ( Effect of Mechanical Stress on Cotton Growth and Development Zhiyong Zhang 0 Xin Zhang 0 Sufang Wang 0 Wanwan Xin 0 Juxiang Tang 0 Qinglian Wang 0 Baohong Zhang, East Carolina University, United States of America 0 School of Life Science and Technology, Henan Institute of Science and Technology , Xinxiang, Henan , China Agricultural crops experience diverse mechanical stimuli, which may affect their growth and development. This study was conducted to investigate the effects of mechanical stresses caused by hanging labels from the flower petioles (HLFP) on plant shape and cotton yields in four cotton varieties: CCRI 41, DP 99B, CCRC 21, and BAI 1. HLFP significantly reduced plant height by between 7.8% and 36.5% in all four lines and also significantly reduced the number of fruiting positions per plant in the CCRI 41, DP 99B and CCRC 21 lines. However, the number of fruiting positions in BAI 1 was unaffected. HLFP also significantly reduced the boll weight for all four cultivars and the seed cotton yields for CCRI 41, DP 99B and BAI 1. Conversely, it significantly increased the seed cotton yield for CCRC 21 by 11.2%. HLFP treatment did not significantly affect the boll count in the fruiting branches of the 1st and 2nd layers in any variety, but did significantly reduce those on the 3rd and 4th fruiting branch layers for CCRI 41 and DP 99B. Similar trends were observed for the number of bolls per FP. In general, HLFP reduced plant height and boll weight. However, the lines responded differently to HLFP treatment in terms of their total numbers of fruiting positions, boll numbers, seed cotton yields, etc. Our results also suggested that HFLP responses might be delayed for some agronomy traits of some cotton genotypes, and that hanging labels from earlyopening flowers might influence the properties related with those that opened later on. - Plants are immobile and therefore unable to escape from threats or unfavorable environments. Consequently, they have evolved diverse mechanisms for coping with and mitigating the effects of various stresses [1]. The adverse effects of disadvantageous environmental conditions, such as excessively high or low temperatures, salt levels, and drought on plant growth and development have been extensively documented. However, the effects of mechanical stresses caused by factors such as wind, rain, physical contact, wounding, and gravity on plant growth and development have not been studied in such detail [2,3]. Agricultural plants are subject to many different kinds of mechanical stress, including shaking [4,5] and bending of their stems [69], rubbing of their stems with fingers [10,11], brushing [12], spraying with water [13,14], mechanical vibration [15], and stress caused by running water [16]. All of these stresses affect plant morphology and development [17]. Different plant species respond to mechanical stress in different ways. Some plants, such as Mimosa pudica, respond rapidly via specialized responsive mechanisms, but others respond slowly [2,18]. In some cases, mechanical stress causes visible phenotypic changes. For example, it has been shown that touching can inhibit growth and retard flowering in Arabidopsis [18]. Similarly, touching was found to reduce the height of cotton plants but did not significantly affect their flowering, the number of bolls they produced, or the cotton yield [4]. In cotton production, it is common to hang labels on flower petioles in order to record the times at which they blossomed and started forming bolls. The mechanical stimulus caused by this practice may affect the growth and development of the cotton plant, but its potential impact has not previously been investigated. Therefore, the work reported herein was conducted to investigate the responses of different cotton genotypes to the mechanical stress caused by hanging labels from cotton flower petioles, in terms of plant shape and yield. Materials and Methods Cotton cultivars Four commercialized transgenic insect-resistant cotton cultivars, CCRI41, DP 99B, CCRC21 and BAI1, were used in this study. CCRI41 was bred by the Cotton Research Institute of the Chinese Academy of Agricultural Sciences; CCRC21 was bred by the Cotton Research Center of the Shandong Academy of Agricultural Sciences; DP 99B was bred by Monsanto Company; and BAI1 was bred by Henan Institute of Sciences and Technology. In China, transgenic insect-resistant cotton cultivars are widely adopted in the yield in recent years. Maybe, insect-resistant gene transformation could result in the different responses of cotton plants to mechanical stress, but it was not in the research scopes of this experiment. Therefore, only transgenic cotton cultivars were used in this experiment. All four cultivars have growth periods of around 130 days. However, CCRI41 and DP 99B cultivars often pre-maturely senesced, BAI1 was resistant to pre-mature senescence, and CCRC21 was in between them. Field experiment The four cotton cultivars were planted in a sandy loam soil with a pH of 8.5 (water: soil = 5 1), an organic matter content of 0.60% (determined by digestion with potassium dichromate under strongly acidic conditions), an available nitrogen content of 18.6 mg kg21 (determined by extraction with 1 M KCl), an available P content of 16.2 mg kg21 (determined by extraction with 0.5 M NaHCO3), and an available K content of 158.5 mg kg21 (determined by extraction with 1 M NH4OAC). Planting was conducted in 2009 and 2010 at the experimental field station (35u169N; 113u569E) of the Henan Institute of Science and Technology, Xinxiang, Henan Province. The cotton seeds were sowed under plastic film mulching, respectively, on April 26th, 2009 and 2010, according to a random block design with four biological replicates. Each block contained 4 plots, and each plot was planted with only one cultivar. Each plot contained four 10 m long rows with an inter-row spacing of 0.8 m and an intra-row spacing of 0.27 m. The planting density was 45,000 plants per hm2. Conventional agricultural practices were applied in the study. 150 kg N, 100 kg P and 75 kg K in the form of urea, diammonium phosphate and potassium sulphate, respectively, were applied per hm2 before sowing. In the early flowering stage, additional quantities of urea-N (150 kg N per hm2) and K (75 kg K per hm2) were applied by top-dressing. All plots were treated with chemical pesticides to keep insects away. Hanging labels from flower petioles (HLFP) During early flowering season, 5 adjacent plants in one of the central rows of each plot were selected and tagged with labels that were hung from their flower petioles during 910 A.M every day and kept in place throughout the blossoming stage. HLFP was made for each flower at its opening day. The anthesis and bollopening dates for the tagged plants were recorded on their labels. A label with a thin thread at its one end weighted 337620 (...truncated)