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  • Author or Editor: Robert E. Wilkinson x
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The influence of two fungicides—captan and thiram—on growth and 45Ca absorption by roots of `Starbrite' watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] seedlings was investigated. Unilateral application of Ca+2 and Al in agar induced curvature in roots from untreated and pretreated seeds. In untreated seeds, PCMBS inhibited Ca+2- and Al-induced root curvature by 82% and 92%, respectively. In commercially pretreated seeds (captan + thiram), PCMBS inhibited Ca+2- but not Al-induced root curvature. Captan or thiram also inhibited Ca+2- or Al-induced root curvature, and the effects of captan and thiram on root curvature were additive. Serial concentration (0, 0.01, 0.1, 1, 10, or 100 mg·liter-1) tests indicated that captan inhibited 45Ca absorption the most at 100 mg·liter-1, whereas thiram inhibited 45Ca absorption the most at 0.01 mg·liter-1. The effects of captan and thiram on 45Ca absorption were statistically additive. Thiram seemed to influence Ca+2 uptake by affecting exofacial sulfhydryl groups (a mode of action similar to that of PCMBS). DTT reversed the inhibitory effect of thiram on 45Ca absorption by 34% but did not reverse the effect of captan. A field test showed that acidic soil (pH 4.55) reduced leaf number; leaf, stem, shoot, and whole-plant dry weights; and stem length of 15-day-old seedlings. Although there was no difference in root dry weights or root: shoot ratios of plants from pretreated and untreated seeds planted in soil at pH 6.26, planting commercially pretreated seeds in acidic soil produced plants with greater root dry weights and root: shoot dry weight ratios than those from untreated seeds. Seedlings showed a greater response to seed treatment in early growth stages. Captan and thiram may have influenced growth characteristics by inhibiting Al uptake of seedlings planted in acidic soil. To our knowledge, this is the first report on the influence of the fungicides captan and thiram on mineral ion uptake in roots. Chemical names used: p-Chloromercuribenzenesulfonic acid (PCMBS), dithiothreitol (DTT), N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (captan), tetramethylthiuram disulfide (thiram).

Free access

Abstract

The inheritance of resistance to Fusarium solani f. phaseoli Kend. & Sny.) in Phaseolus vulgaris lines P. I. 203958 (N203), and 2114-12 which derives its resistance from P. coccineus, was studied under greenhouse and field conditions. It was concluded that: N203 and 2114-12 respectively possess 4 and 5-6 genes for resistance under the greenhouse-test conditions used; 4 of the 2114-12 genes for resistance are the same as the N203 genes; gene action is mostly additive but partial dominance of resistance appears in 9-13-week-old field-tested plants. Broad sense heritability was estimated as 62-64% under greenhouse conditions and as 22% and 79%, respectively, in 5 and 9-13-week-old field tested plants. The additive variance under greenhouse conditions was estimated as 72% and 40% respectively for resistance from 2114-12 and N203.

Open Access

Abstract

Resistance to T. basicola was found in Phaseolus vulgaris lines P.I.203958 (N203) and 2114-12. To determine the inheritance of resistance, these 2 lines were crossed with each other and with the susceptible cv. Redkote. Greenhouse tests were conducted on parental, F1, F2, and backcross progenies of each of the 3 crosses, and on F3 progenies of crosses ‘Redkote’ × 2114-12 and ‘Redkote’ × N203. The data indicate that N203 and 2114-12 possess the same genes for resistance, that resistance is partially recessive, and that resistance is controlled by approximately 3 genes. Broad sense heritability was estimated as 59% and the additive variance as 39%.

Open Access

Abstract

Previous reports suggest similarity between Fusarium and Thielaviopsis root rot resistances in beans (Phaseolus vulgaris L.), with regard to both source and nature of resistance. This study was conducted to determine the relationship between the genes controlling resistance to the 2 pathogens. The susceptible cultivar ‘Redkote’ was crossed with bean lines 2114-12 and P.I. 203958 (N203), both of which have resistance to Fusarium and Thielaviopsis. Four populations of F6 lines were separately developed. Two populations were derived from ‘Redkote’ × 2114-12; one was selected for resistance to Fusarium and the second for resistance to Thielaviopsis. Similarily, a Fusarium-resistant and also a Thielaviopsis-resistant population of F6 lines were derived from ‘Redkote’ × N203. Two additional populations of F4 plants, one resistant to Fusarium and one resistant to Thielaviopsis, were derived from the backcross [(‘Redkote’ × 2114-12, F2) × ‘Redkote’]. The F6 and F4 lines developed for resistance to Fusarium or to Thielaviopsis were subsequently tested for resistance to the other pathogen. The data indicate that genes controlling resistance to Fusarium and Thielaviopsis are different and non-linked.

Open Access

Watermelon [Citrullus lanatus (Thumb) Matsum and Nakai] cultivars Charleston Gray(CG), Crimson Sweet(CS), Dixielee(DL), Jubilee(JL), Mirage(MG) and Starbrite(SB) were grown in white quartz flintshot sand and watered daily with 0.01M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, 6.0, or 6.5. After two weeks, stem length, leaf area, leaf and root dry weight, and root number were measured. Nnumber of root decreased with decreasing pH below pH 5.0 in all cultivars except CG, which had an increase trend. Root number of MG and SB had negative linear and quadratic correlations respectively, with decreasing pH. In all cultivars, root dry weight increased with decreasing pH below pH 5.5. Under pH≤4.5, all cultivars except CG, had short or no tap root and thickened lateral roots. CG had a decrease in stem length, leaf dry weight and leaf area with increasing pH, and was sensitive to high pH. However, MG and SB had reduction in leaf area and stem length with decreasing pH, which suggests that MG and SB are sensitive to low pH. Although there were no differences in shoot parameters of 2wk-old plants of CS, DL and JL, observations made at 7 days after seeding indicated a possible pH effect on early growth of seedling.

Free access

Unilateral application of Ca2+ and Al3+ induced curvature in roots of `Starbrite' watermelon [Citrullus lanatus (Thumb.) Matsum and Nakai] seedlings from both untreated and commercially pretreated seeds. In untreated seeds, PCMBS inhibited root curvature by decreasing Ca2+ and Al3+ uptake. In pretreated seeds, PCMBS only inhibited Ca2+-induced root curvature. Captan and thiram inhibited Ca2+- or Al3+-induced root curvature. Captan showed the greatest inhibition of Ca2+ uptake at 100 mg/liter, whereas thiram was most effective at 0.01 mg/liter. The effects of captan and thiram were statistically additive. Thiram appeared to show a similar mode of action to PCMBS in affecting Ca2+ uptake. DDT reversed the inhibitory effect of thiram, but not that of captan.

Acid soil (pH 4.6) reduced number of leaves, leaf, stem, shoot and whole plant dry weight, and stem length. Pretreated seeds produced greater root dry weight and root:shoot ratio in acid soil than did untreated seeds. Fungicides may have reduced Al3+ toxicity by inhibiting Al3+ uptake in acid soil.

Free access