In this study, we carried out phenotypic, physiological, biochemical, analysis, and field regeneration capacity for 21 accessions of the upland cotton and also used callus induction of the same 21 accessions on hypocotyl, cotyledons, and shoot tip tissues to check the regeneration of shoots and roots from these three tissues to validate the field regeneration capacity of each accession. The height of cotton plants is a result of active cell division and favorable weather conditions for appropriate growth and development. Plant height gives a good affinity to light intensity and in turn proper photosynthesis. According to our finding, three accessions (JiMian863, LuMian378, and LuMian319) were discovered to have the highest plant height than other accessions. Light is a source of energy as well as an important signal for environmental changes, causing a variety of physiological reactions in plants (Abidi et al. 2013). According to the previous report it was revealed that photoperiod significantly influenced photosynthesis, seed germination, breaking of dormancy, and the flowering process (Skjelva 2004; Rezazadeh and Harkess 2018). Our finding revealed that there is a significant correlation between plant height and leaf area on ZS065 accession, this trait (height) has a significant role in the growth and development of upland cotton due to large leaf area to trap enormous sunlight, It was reported that plant height is an important selection target since it is associated with yield potential, stability, and particularly with lodging resistance in various environments (Hassan et al. 2019). Flowering onset time has been reported to be positively correlated with maximum plant height (Hmax). Herbaceous grassland species, taller species often flower later than shorter ones (Dahlgren et al., 2007). On the JiMian863 accession, we discovered a significant relationship between leaf area and plant height. In the JiMian863 accession, there is new shoot regeneration in callus induction.
Low leaf area and leaf branches were observed on JunMian1Hao accession, which corresponds to a high level of carotenoid. This could be due to the low amount of sunlight strike the surface of leaves. The concentration of photosynthetically active pigments increases in carotenoid content under the shade condition and this is applied to chlorophylls and carotenoids in green algae (Czeczuga 1987). There is a significant correlation between shoot tip callus induction and shoot regeneration capacity on JunMian1Hao. Low moisture content and low conductivity were observed on JunMian1Hao accession. The high percentage of re-generable embryogenic calli is a prerequisite for genetic manipulation towards varietal improvement. This study aimed to test and improve the embryogenic potential of calli for better plant regeneration efficiency (Juturu et al. 2016). Flower and boll number is an important trait for upland cotton. A large number of boll produces enormous fiber contents. Three accessions were found to have the highest number of flowers and bolls (Bole34 and Dai15) in comparison to new tissue regeneration on these accession new shoot and root were observed in cotyledon and shoot tip tissues. This is an indication that good callus induction induces new tissues regeneration in shoot tip and cotyledon tissues of Bole34 and Dai15 accessions.
Moderate callus induction was observed on LuMian319 accession for shoot tip tissue with a significant correlation for shoot regeneration. For the same Bole34 accession, there was the highest shoot tip callus induction (100%), which correlates with shoot regeneration, similar findings for root regeneration of cotyledon tissue similarly hypocotyl and shoot tip tissues produce a new shoot tissue. Multiple shoot and root regeneration correlates with the maximum callus induction capacity. In the field, three accessions were also discovered to have limited or low flower and boll (JunMian1Hao and FH682) with no new leaf produce in some accessions. Callus induction capacity was used to confirm the new tissues regeneration levels on these accessions. Shoot tip callus induction with corresponding shoot regeneration was observed on JunMian1Hao accessions. Low leaf branches, low moisture content, and low conductivity were observed on JunMian1Hao accession, this may be attributed to the effects of moisture on conductivity level. Thermal conductivity depends on temperature and moisture content. In comparison shoot, tip callus induction (100%) correlates with good shoot regeneration capacity on FH682. In hypocotyl callus induction high callus (100%) response was observed on nine accessions which also correlates with shoot regeneration in 12 accessions. There is a similarity between callus induction and new tissue (shoots and roots) regeneration observed in hypocotyl in seven accessions (ZS061, Ari971, Esha218Hao, 2019Y-3, LuMian378, ZS065, and LuMian319). It was also discovered that accessions with low flower and boll numbers in the field correlate with a low callus induction level and low regeneration capacity in hypocotyl tissue (JunMian1Hao and ZhongMianSuo24), the same accession also displays a limited response to regeneration capacity. Our finding also revealed that callus induction abilities are greatly influenced by the genotype and are in agreement with the previously reported work in Oryza sativa (Abe and Futsuhara 1986). Culture medium composition, genotype, and its condition are important factors affecting callus induction and its regeneration rate. Among those factors, the genotype appears to be a more important factor affecting the efficiency of in vitro culture. In Triticum aestivum, the explants with the same age and the same growth regulator combination, callus production and plant regeneration capacity depend essentially on genotype (Arzani and Mirodjagh 1999). Fruit branches is an important trait for upland cotton, the quality of cotton fiber results from an interaction between environmental, genetic, and management factors, determined by the position of the resources obtained by each fruit (Percy et al. 2006; Girma et al. 2007).
Cotton morphology is primarily determined based on flowering and shoot branching patterns which directly influence sunlight distribution, yield, planting area, the efficiency of harvest mechanization, and the cost of planting (Reinhardt and Kuhlemeier 2002; Sakamoto and Matsuoka 2004). The net weight of each leaf of the 21 accessions was weighed and determined. the water retention capacity, which was used to determine the relative amount of water which indicates drought resistance levels of each accession. According to the mean comparison values, two accessions (ZS065 and ZS061) have the strongest affinity for drought resistance than the rest of the accessions. Similarly, the lowest affinity to drought resistance was observed on (BeiZheGongSheMian and LiaoYangDuoMaoMian) according to mean comparison values. In LuMian319 accession, a significant correlation was observed for both moisture content and net conductivity. This is possibly due to genetic variation in the genome constituent within the Gossypium hirsutum. It was reported that plants are evolved to regulate growth periods to avoid moisture stress, termed as drought escape (Manavalan et al. 2009). The first response of plants to drought as a drought-resistance strategy relies on avoiding water deficit (Zonta et al. 2017). by maintaining tissue weight through increasing water uptake or restricting water loss (Antunes et al. 2018). Leaf conductivity was asses for membrane stability on 2019Y-3 accession and it was found out that it correlated with higher chlorophyll content and it’s also similar a related finding that photosynthetic stimulation was correlated with increased leaf conductance (Chen 2000).
Carotenoid content which functions in trapping the sunlight for photosynthesis, the values of each accession were measured and recorded. There was a significant correlation on the value of carotenoid in comparison to other traits. On rare finding high carotenoid content correlated with high values of chlorophyll content on (N98-283, ZS061 and Si-6524) accessions respectively. Cotton which attained a required height doesn’t necessarily need high carotenoid content to trap more sunlight to attain maximum growth. High carotenoid content was recorded on N98-283 accession (2.0377) with low cotton height, in comparison to other accessions with the low value of carotenoid so high carotenoid content doesn’t necessarily correlate with good height and this can be supported on view to the intensity of plant height which increased at low light intensity (Wang and Li 2008). Proline is an important trait in Gossypium hirsutum which overcome biotic and abiotic stresses. In comparison for Proline levels among 21 accessions, it indicated that JunMian1Hao accession has the highest Proline content and low-moderate moisture content and this support the finding that plants were subjected to a drying cycle when the plants have four true leaves and the Proline content of the leaf tissue was determined (Chen 1966). In callus induction and new tissue regeneration, there are so many correlations among the 21 accessions. Nine accessions have 100% callus induction capacity for hypocotyl tissue in comparison to the regeneration capacity and callus induction on hypocotyl tissue, no callus induction formed below 50% was observed in all the three tissues (hypocotyl, cotyledons and shoot tip). The highest callus induction was observed in shoot tip tissue and this is possibly due to the presence of meristematic cells at the tip end of the seedling in Gossypium hirsutum. It was reported that high percentage of re-generable embryogenic calli is a prerequisite for genetic manipulation towards varietal improvement (Juturu et al., 2016). Embryogenic callus is best requirement for successful tissues regeneration. Successful callus induction and subsequent tissues regeneration depends on exogenous supply of plant hormones (Rueb et al. 1994; Samota et al. 2017)