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Fusarium wilt (Fusarium oxysporumf. sp. vasinfectumrace 4, FOV4) in cotton is an early season soil‐borne vascular disease including seedling wilt and death. Its infection process in Upland cotton is currently unknown. This study compared the infection process among three Upland cotton cultivars (Gossypium hirsutum) using a confocal microscope. Seedlings were grown in a hydroponic system to the two‐true leaf stage and inoculated with a virulent local FOV4 isolate. Based on the infection process, the resistant cultivar FM 2334GLT was divided into resistant (R) and susceptible (S) groups. The susceptible PHY 725 RF and FM 2334GLT(S) had the highest numbers of conidia attached and germinated on the root surface, followed by susceptible Acala 1517‐08. FM 2334GLT(R) had the lowest numbers. Hyphae penetration and colonization inside the root followed a similar trend. In PHY 725 RF, FM 2334GLT(S), and Acala 1517‐08, hyphae started to penetrate into epidermal cells at 2 days post inoculation (dpi), spread in the cortex intercellularly and intracellularly at 3–5 dpi, and entered the xylem vessels at 7 dpi, followed by colonization at 11–15 dpi. FM 2334GLT(R) had the lowest numbers of penetrating hyphae inside the root, with no apparent hyphae observed in the xylem. This study demonstrated that FM 2334GLT(R) had delayed infection, reduced fungal growth and reproduction, and prevented the FOV4 fungus from invading the xylem. The resistance in FM 2334GLT(R) was similar to that in Pima PHY 841 RF but with fewer hyphae in the cortex, suggesting possible different resistant mechanisms. FM 2334GLT is a known Upland cotton with resistance to Fusarium wilt race 4 (FOV4).It is divided into the resistant (R) and susceptible (S) groups based on the infection process.FM 2334GLT(R) had the lowest FOV4 conidia attached/germinated on the root surface compared to susceptible lines.FM 2334GLT(R) had the lowest penetrating hyphae inside the root, with no apparent hyphae observed in the xylem.FM 2334GLT(R) delayed infection, reduced fungal growth and reproduction, and prevented FOV4 from invading the xylem.

Fusarium wilt caused by soil‐borne fungus Fusarium oxysporumf. sp. vasinfectumrace 4 (FOV4) is an early season disease causing root rot, and seedling wilt and death. However, it was unknown if cotton (Gossypiumspp.) growth stages and root wounding affected genotypic responses to FOV4. The objectives of this study were to investigate the effects of cotton growth stage, cultivar, and root wounding on FOV4‐associated disease development at 7‐, 14‐, 21‐, and 28‐d post inoculation through five replicated tests in controlled environmental conditions with temperatures at 21 to 23 °C. Seedlings inoculated at the cotyledon stage incurred the highest disease incidence (DI), disease severity rating (DSR), and mortality (MR), followed by seedlings inoculated at the 1‐, 3‐, and 5‐true leaf stages in descending order. Root wounding at the cotyledon stage followed by immediate inoculation with FOV4 inoculum made all the tested cultivars and lines highly susceptible. Among the six cultivars tested, FM 2334GLT and Pima DP 359 RF were the most resistant, Pima S‐7 was highly susceptible, and Acala 1517‐08, Acala 1517–18 GLS, and Pima PHY 881 RF were susceptible. The importance of artificial inoculation at a true leaf stage with or without root wounding to identify resistance that may be undetected under field conditions was discussed. Five replicated, controlled‐environment tests were conducted at 21 to 23 °C temperatures.Cotyledon stage seedlings were most susceptible to FOV4, followed by the 1‐, 3‐, and 5‐true leaf stages.Root wounding disarmed resistant mechanisms provided by the root and made all tested lines susceptible.FM 2334GLT and Pima DP 359 RF were the most resistant among the lines tested.Artificial inoculation at true leaf stages may identify resistance that may be undetected in the field.

Fusarium wilt, caused by Fusarium oxysporumf. sp. vasinfectumrace 4 (FOV4), is an early season vascular disease with symptoms including seedling wilt and mortality. The objectives of this study were to investigate the relationship between mortality rate (MR) and disease severity rating (DSR) based on root vascular staining (RVS)‐DSR and stem vascular discoloration (SVD)‐DSR in the field and the relationship of MR in controlled conditions with MR and DSR in the field. Results from two field tests and two greenhouse tests each with a Latin square design for eight cultivars of cotton (Gossypiumspp.) and two field progeny‐row tests were analyzed. In the field, MR at the square stage was significantly correlated with both DSR (RVS) and DSR (SVD) at crop maturity, and they were also significantly correlated with DSR based on both MR and RVS‐DSR (MR+RVS) and both MR and SVD‐DSR (MR+SVD). The results show that DSR (MR+RVS) was the most accurate in assessing FOV4 resistance, and DSR (SVD) and DSR (MR+SVD) can be used in combination with DSR (RVS) and DSR (MR+RVS), or as the substitutes for RVS. Mortality rate in the greenhouse was significantly correlated with MR and DSR (MR+RVS) and DSR (MR+SVD) in the field, indicating consistency between evaluations under both conditions. Furthermore, foliar symptoms‐based MR and DSR under controlled‐conditions were significantly correlated, with coefficients of variation at 20 to 30% in other related studies. The results confirm the validity of using the two parameters in greenhouse evaluations for FOV4 resistance in cotton. Mortality rate at the square stage is significantly related with RVS at crop maturity.Mortality rate is significantly correlated with SVD at crop maturity.Root vascular staining is highly significantly correlated with SVD.Disease severity rating combining MR and RVS or SVD is the most reliable in assessing resistance to race 4.Mortality rate in the greenhouse is significantly correlated with MR and DSR in the field.

Fusarium oxysporumf. sp. vasinfectumRace 4 (FOV4) causes high seedling mortality in pima cotton (Gossypium barbadenseL.) grown in the western and southwestern U.S. Cotton Belt. The objectives of this study were to analyze the combining abilities and genetic basis of FOV4 resistance in pima cotton using a half‐diallel mating design. Thirty‐six biparental F3and F4generations were derived from six commercial cultivars and three elite lines and artificially inoculated with FOV4 for screening for FOV4 resistance in four replicated tests, with two tests for each generation. Disease severity rating (DSR) at 28 d after inoculation (DAI) and the area under the disease progress curve (AUDPC) across 7, 14, 21, and 28 DAI were analyzed via Griffing's Method 2 and Hayman's diallel analysis. ‘Pima S‐6’, ‘PHY 76’, and ‘8810’ (resistant parents) were heterogeneous in their responses to FOV4 infections with 20 to 50% disease incidence and mortality rate; and they had significantly lower DSR and AUDPC with negative general combing ability effects compared with the susceptible parents. Variances caused by specific combining ability and nonadditive effects were higher than those caused by additive effects for FOV4 resistance, consistent with the estimates for broad‐sense heritability. The results indicated a predominant nonadditive effect for FOV4 resistance within these genotypes of pima cotton. A minimum of one or two genes was estimated for FOV4 resistance based on Hayman analysis. The results represented the first study applying a diallel analysis to investigate the quantitative genetic basis of FOV4 resistance in pima cotton. Thirty‐six hybrids in F3and F4generations were made from nine pima lines.The hybrids & parents were artifically evaluated for Fusariumwilt race 4 (FOV4) resistance.Three pima parents were moderately resistant to FOV4.The three parents exhibited negative general combing ability effects on FOV4 resistance.The variance caused by nonadditive effects had a more important role than additive effects.

In an effort to better understand the mechanisms that regulate oil accumulation and packaging in seeds, transgenic cotton lines were generated using a Brassica napusnonfunctional delta‐12 fatty acid desaturase (FAD2) gene under control of the phaseolin promoter. Seeds of numerous transgenic plant lines had reduced oil content compared with null‐segregating siblings or nontransformed seeds. Seed oil content was quantified by 1H‐NMR, and was reduced to 12% or less of seed weight in transgenics from 20% by weight in nontransformed controls. Light‐ and electron‐microscopic analyses of severely lowered lines, showed a reduction in overall cotyledon thickness and a disruption in cellular and subcellular organization. Lipid bodies and protein bodies were fewer in transgenics, and their size and distribution in cells was different than that in nontransformed seeds. Coincident with reduced storage reserves, sucrose levels were elevated in transgenic seeds. The overall effect of oil suppression was to selectively reduce the size of the embryo, but the seed coat and fiber properties remained unaffected in seeds. In fact there was a significant increase in lint percentage in all oil‐suppressed lines examined. Overall we propose that expression of the nonfunctional Bnfad2allele in cottonseeds disrupts normal oil biosynthesis and provides for redirection of carbon reserves.

Fruiting of cotton (Gossypium hirsutumL.) was evaluated by main stem node and branch position in 11 experiments over a 4‐yr period to determine if mepiquat chloride (MC) (1,1‐dimethylpiperidinium chloride) altered fruiting position development or retention. Fruiting events were monitored for main stem nodes 7 to 20 for first fruiting position on sympodial branches (SB1), secondary fruiting positions on sympodial branches (SB>1), and fruiting positions on monopodial branches (MB). Ten consecutive plants were plant mapped from each of four replications in each experiment and combined as a 40‐plant total for analysis of treatment and node effects using experiments as replications. Mepiquat chloride was applied at 49 g ha−1when average plant height was 0.57 m and plants averaged 0.9 white blooms m−2. Summed across nodes, plant zones SB1, SB>1, and MB accounted for 60, 26, and 13% of all harvestable bolls, produced 37, 46, and 17% of all fruiting positions, and set 45, 16, and 23% of all fruiting positions as harvestable bolls, respectively. Application of MC did not increase total number of bolls. The interaction of MC treatment and nodes was significant for SB1 and SB>1, with MC treated plants setting more bolls at lower nodes but fewer at upper nodes. The maximum cumulative benefit occurred at node 12 where MC treated plants had 15% more bolls matured than control plants (58.3 and 50.6 bolls m−2, respectively). This advantage from MC treatment was not maintained as upper nodes matured fewer bolls than control plants. Plants treated with MC produced 3.1% fewer (P = 0.07) fruiting positions than control plants (288 and 279 m−2respectively). Treatment by node interactions were significant for SB1 and SB>1, with MC increasing fruiting positions up to node 15 at SB1 and up to node 9 for SB>1, but having fewer at the remaining nodes. Early boll load was stimulated by MC. Late season boll load was decreased, apparently not by limited initiation of fruiting positions, but rather by increased abortion of fruiting forms. Use of MC according to the rate and timing of these tests would be of benefit when length of the season is a primary constraint to yield potential. In full‐season, non‐rank cotton, however, the early benefit in boll load is lost.