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M.R. Foolad and G.Y. Lin

The genetic relationship between cold tolerance (CT) during seed germination and vegetative growth in tomato (Lycopersicon esculentum Mill.) was determined. An F2 population of a cross between accession PI120256 (cold tolerant during both seed germination and vegetative growth) and UCT5 (cold sensitive during both stages) was evaluated for germination under cold stress and the most cold tolerant progeny (the first 5% germinated) were selected. Selected progeny were grown to maturity and self-fertilized to produce F3 families (referred to as the selected F3 population). The selected F3 population was evaluated for CT separately during seed germination and vegetative growth and its performance was compared with that of a nonselected F3 population of the same cross. Results indicated that selection for CT during seed germination significantly improved CT of the progeny during germination; a realized heritability of 0.75 was obtained for CT during seed germination. However, selection for CT during germination did not affect plant CT during vegetative growth; there was no significant difference between the selected and nonselected F3 populations in either absolute CT [defined as shoot fresh weight (FW) under cold stress] or relative CT (defined as shoot FW under cold as a percentage of control). Results indicated that, in PI120256, CT during seed germination was genetically independent of CT during vegetative growth. Thus, to develop tomato cultivars with improved CT during different developmental stages, selection protocols that include all critical stages are necessary.

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M.R. Foolad and G.Y. Lin

Cold tolerance (CT) of 31 tomato accessions (cultivars, breeding lines, and plant introductions) representing six Lycopersicon L. sp. was evaluated during seed germination and vegetative growth. Seed germination was evaluated under temperature regimes of 11 ± 0.5 °C (cold stress) and 20 ± 0.5 °C (control) in petri plates containing 0.8% agar medium and maintained in darkness. Cold tolerance during seed germination was defined as the inverse of the ratio of germination time under cold stress to germination time under control conditions and referred to as germination tolerance index (TIG). Across accessions, TIG ranged from 0.15 to 0.48 indicating the presence of genotypic variation for CT during germination. Vegetative growth was evaluated in growth chambers with 12 h days/12 h nights of 12/5 °C (cold stress) and 25/18 °C (control) with a 12 h photoperiod of 350 mmol.m-2.s-1 (photosynthetic photon flux). Cold tolerance during vegetative growth was defined as the ratio of shoot dry weight (DW) under cold stress (DWS) to shoot DW under control (DWC) conditions and referred to as vegetative growth tolerance index (TIVG). Across accessions, TIVG ranged from 0.12 to 0.39 indicating the presence of genotypic variation for CT during vegetative growth. Cold tolerance during vegetative growth was independent of plant vigor, as judged by the absence of a significant correlation (r = 0.14, P > 0.05) between TIVG and DWC. Furthermore, CT during vegetative growth was independent of CT during seed germination, as judged by the absence of a significant rank correlation (rR = 0.14, P > 0.05) between TIVG and TIG. A few accessions, however, were identified with CT during both seed germination and vegetative growth. Results indicate that for CT breeding in tomato, each stage of plant development may have to be evaluated and selected for separately.

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Shuyin Liang, Xuan Wu, and David Byrne

This project examined rose (Rosa ×hybrida) performance by measuring flower size and flower numbers per inflorescence in spring, summer, and fall seasons (mean temperatures 21.7, 30.0, and 18.1 °C, respectively) in interrelated rose populations. Populations and progeny differed in flower size as expected. Heat stress in the summer season decreased flower diameter (18%), petal number (17% to 20%), and flower dry weight (32%). Analysis of variance (ANOVA) showed a significant population/progeny × heat stress interaction for flower diameter indicating that rose genotypes responded differentially to heat stress. Flower size traits had moderate low to moderate narrow-sense (0.38, 0.26–0.33, and 0.53 for flower diameter, petal number, and flower dry weight, respectively) and moderately high to high broad-sense (0.70, 0.85–0.91, and 0.88 for flower diameter, petal number, and flower dry weight, respectively) heritability. Genotype × environment (G × E) variance (population/progeny × heat stress) for flower diameter accounted for ≈35% of the total variance in the field experiment indicating that heat stress had moderate differential genotypic effects. However, the genetic variance was several fold greater than the G × E variance indicating selection for flower size would be effective in any season but for the selection of a stable flower size (heat tolerant) rose genotype, selection would be required in both the cool and warm seasons. Seasonal differences in flower productivity of new shoots did not appear related to heat stress but rather to the severity of pruning conducted in the different seasons. The number of flowers produced on the inflorescence had moderate narrow-sense (h 2 = 0.43) and high broad-sense (H 2 = 0.75) heritability with a moderate genotype × pruning effect that explained about 36% of the variance.

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Jean Carlos Bettoni, Aike Anneliese Kretzschmar, Remi Bonnart, Ashley Shepherd, and Gayle M. Volk

repositories. Field maintenance is costly and time-consuming, it requires extensive acreage, and plants are vulnerable to abiotic stresses and biotic threats ( Benelli et al., 2013 ; Marković et al., 2013b ; Pathirana et al., 2016 ). In vitro culture back

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Erick Amombo, Huiying Li, and Jinmin Fu

( Blumwald, 1987 ; Cabot et al., 2009 ; Dodd et al., 2010 ; Harper et al., 2004 ; Kanchiswamy et al., 2010 ; Sheen, 1996 ; Srivastava et al., 2013 ). Intracellularly, Ca 2+ serves as a secondary messenger during abiotic stress signaling ( Chidananda et

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R. Karina Gallardo, Parichat Klingthong, Qi Zhang, James Polashock, Amaya Atucha, Juan Zalapa, Cesar Rodriguez-Saona, Nicholi Vorsa, and Massimo Iorizzo

anthocyanin content; and 4) disease resistance. However, there is a growing need to focus on other traits, such as tolerance to pest and abiotic stress, as well as to effectively pyramid multiple traits, as they become relevant to the success of the industry

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Sylvia Cherono, Charmaine Ntini, Misganaw Wassie, Mohammad Dulal Mollah, Mohammad A. Belal, Collins Ogutu, and Yuepeng Han

radioimmunoassay ( Hattori et al., 1995 ), and many studies have been carried out to elucidate its functions in regulating growth. Melatonin has been associated with plant protection against biotic and abiotic stress as an antioxidant ( Afreen et al., 2006 ). For

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Qing Xu, Shi-Rong Guo, He Li, Nan-Shan Du, Sheng Shu, and Jin Sun

Grafting of vegetable seedlings is widely used in horticulture for various reasons, such as managing soil-borne disease and improving crop responses to abiotic stresses. Ling et al. (2013) suggested that watermelon wilt ( Fusarium oxysporum f. sp

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Xiaobo Sun, Yanming Deng, Lijian Liang, Xinping Jia, Zheng Xiao, and Jiale Su

( Alexandersson et al., 2010 ; Luu and Maurel, 2005 ). The latter is more efficient in regulating water transport across membranes when plants are experiencing abiotic stresses ( Lian et al., 2004 ; Vera-Estrella et al., 2004 ). The symplastic pathway is

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Weijie Jiang, Jie Bai, Xueyong Yang, Hongjun Yu, and Yanpeng Liu

) were also shown to be involved in low-temperature response ( Cuevas et al., 2008 ; Kagale et al., 2007 ). Abscisic acid is the central regulator of abiotic stress resistance in plants and is involved in many stress responses. A plant's ABA content