Gossypium hirsutum races are believed to be potential reservoirs of desirable traits, which can play crucial roles to overcome the existing narrow genetic base of modern Upland cotton cultivars.  However, prior to utilizing the races in cotton improvement programs, understanding their genetic constitutions is needed.  Thus, this study used molecular and morphological techniques to characterize 110 G. hirsutum germplasm including 109 semi-wild accessions and one Upland cotton cultivar, CRI12.  In the study, 104 SSR markers detected 795 alleles, with an average of 7.64 alleles per marker, ranging from 3 to 14, and average polymorphism information content (PIC) value of 0.71.  And 96 of the markers were found to be highly informative, with PIC value≥0.50.  Pairwise genetic similarity coefficient across the accessions ranged from 0.19 to 1.00, with an average value of 0.46.  Morphological characterization was done using fiber length, fiber strength, micronaire, fiber uniformity index, and fiber elongation.  Pairwise taxonomic distance within the accessions ranged from 0.17 to 3.41, with a mean of 1.33.  The SSR and fiber quality traits data set based unweighted pair group method of arithmetic mean (UPGMA) analysis grouped the accessions into 7 and 12 distinct clusters, respectively, that corresponds well with the results of principal component analysis (PCA).  Our study revealed the existence of vast molecular and morphological diversities within the accessions and provided valuable information on each semi-wild accession for quick and better informed germplasm utilization in cotton breeding programs.   

    Alkaline soils have a great influence on apple production in Northern China. Therefore, comprehensive evaluations of tolerance to such stress are important when selecting the most suitable apple rootstocks. We used hydroponics culturing to test 17 genotypes of apple rootstocks after treatment with 1:1 Na₂CO₃ and NaHCO₃. When compared with the normally grown controls, stressed plants produced fewer new leaves, and had shorter roots and shoots and lower fresh and dry weights after 15 d of exposure to alkaline conditions. Their root/shoot ratios were also reduced, indicating that the roots had been severely damaged. For all stressed rootstocks, electrolyte leakage (EL) and the concentration of malondialdehyde (MDA) increased while levels of chlorophyll decreased. Changes in root activity (up or down), as well as the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were rootstock-dependent, possibly reflecting their differences in alkali tolerance. Using alkali injury index (AI), adversity resistance coefficients (ARC), cluster analysis, and evaluation of their physiological responses, we classified these 17 genotypes into three groups: (1) high tolerance: Hubeihaitang, Wushanbianyehaitang, Laoshanhaitang Ls2, Xiaojinbianyehaitang, and Fupingqiuzi; (2) moderate tolerance: Pingyitiancha, Laoshanhaitang Ls3, Hubeihaitang A1, Deqinhaitang, Balenghaitang, Maoshandingzi, Shandingzi, and Xinjiangyepingguo; or (3) low tolerance: Pingdinghaitang, Hongsanyehaitang, Xiaojinhaitang, and Sanyehaitang. These results will significantly contribute to the selection of the most suitable materials for rootstocks with desired levels of tolerance to alkali stress.

Telomeres form the ends of eukaryotic chromosomes and serve as protective caps that keep chromosomes structure independency and completeness. The first plant telomere DNA was isolated from Arabidopsis thaliana and was shown to have tandemly repeated sequence 5´-TTTAGGG-3´. The Arabidopsis-type telomere has been found in many plants, but several reports indicate that this sequence is absent in some plants. Up to now, no research has been conducted on the telomere of cotton. In this paper, the Arabidopsis-type telomere sequence was amplified and cloned using the primers designed based on the fragment containing telomere sequence in an Arabidopsis bacterial artificial chromosome (BAC). Fluorescence in situ hybridization (FISH) with cotton metaphase chromosomes using the Arabidopsis-type telomere sequence as probes indicated that the signals were located at all chromosome ends of seven diploid and two tetraploid cotton species with different signal intensities among chromosome complements of different cotton species, even between long and short arms of the same chromosome. To identify the signals of FISH, the genome DNA of Xinhai 7, a cultivar of Gossypium barbadense, digested by BAL-31 nuclease was introduced in this study. The result of BAL-31 digestion indicated that the hybridization signals of FISH represent the outermost DNA sequence of each cotton chromosomes. So we first proved that the telomeric repeats of cotton cross-hybridize with that of Arabidopsis. The results of terminal restriction fragment (TRF) showed significant variation in telomere length among cotton species. The telomere length of cultivated cotton was close to 20 kb and was larger than those of wild cotton species whose telomere length ranged from 6 to 20 kb.