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Abstract
Seedlings of snap bean (Phaseolus vulgaris L.) ‘Strike’ and ‘Kentucky Wonder’ were inoculated with 0, 6,000, 12,000, or 18,000 Meloidogyne hapla (Chitwood) larvae/pot. Leaf xylem potential, stomatal conductance, transpiration, root hydraulic conductivity, leaf area, and plant weight were measured 4 weeks after inoculation. In a 2nd experiment, inoculated plants were grown for 7 weeks to obtain yield data. Leaf area, xylem potential, and yield were significantly reduced by nematode infection. The 2 cultivars differed in their response to M. hapla. Yield was reduced more at high nematode populations in ‘Kentucky Wonder’ than in ‘Strike’. This differential response also occurred with xylem potential. There was a trend toward decreased hydraulic conductivity in infected ‘Kentucky Wonder’, but not ‘Strike’ roots. Cultivar tolerance in beans appears to be related to the effects of nematodes on plant water relations.
Abstract
Seedlings of the snap bean (Phaselous vulgaris L.), cv. Kentucky Wonder, were inoculated with ≈0, 240, 2400, or 24,000 root knot [Meloidogyne hapla (Chitwood)] nematodes per plant and grown in a sandy soil in the greenhouse at a soil water potential of either −0.025 (high soil moisture) or −0.075 (low soil moisture) MPa. Leaf xylem potential, transpiration, root hydraulic conductivity, and nematode populations in roots, as well as growth and yield data, were collected about 8 weeks after inoculation. Transpiration was reduced by decreasing soil moisture—maximum transpiration occurred about midday at high soil moisture and in the early morning at low soil moisture. Transpiration decreased late in the day with increasing nematode populations at high, but not low, soil moisture. Leaf xylem potential was reduced by low soil moisture and nematodes but interactive effects were not significant. Root conductivity was lower in plants exposed to low soil moisture than in plants maintained at high soil moisture. However, nematodes reduced conductivity in only one of two experiments, and interactive effects were not significant in either experiment. Root and shoot dry weight and leaf area were decreased in response to low soil moisture. Nematodes reduced shoot dry weight and leaf area, but not root dry weight, in one of two experiments and there were no significant interactive effects in either experiment. Total yields of beans were reduced at low soil moisture and in response to nematode inoculum. A significant interactive effect on early bean yield was also evident; nematodes lowered early yields more at high soil moisture than at low soil moisture. These data indicate that although soil moisture and M. hapla populations individually influenced water relations, growth, and yield of bean, the interactive effects were generally not significant. When an interaction could be demonstrated, it was due to a decreased effect of nematodes at low soil moisture.
Abstract
‘Miragreen’ garden pea seeds from individual seed lots were sorted into bleached, partially-bleached, and non-bleached categories. Seeds were either soaked for 48 hours in aerated water at 22°C, coated with thiram fungicide, or received no treatment. Seeds were planted in Conover loam soil where damping-off and seedling rot were primarily caused by Pythium ultimum Trow and Fusarium solani (Mort.) Sacc f. sp. pisi (Jones) Snyd. & Hans. No differences in germination in vitro were found among bleached, partially bleached, and non-bleached seeds. However, seedling emergence in the field was greater from untreated non-bleached seeds (69%) than from untreated bleached seeds (30%); emergence from partially bleached seeds (58%) was intermediate. Regardless of degree of bleaching, all seedlings were a normal green color after emergence, and appeared equal in vigor. Pea yields from untreated bleached seeds were less than from untreated non-bleached seeds, apparently because pea-emergence damping off was so much greater with bleached than with non-bleached seeds. No yield differences occurred with fungicide-treated seeds. Soaking partially bleached seeds for 48 hours in aerated water at 22°C prior to planting in April was as effective in improving emergence in artificially infested soil as coating seeds with thiram. However, when seeds were planted in mid-June, the thiram treatment gave higher seedling emergence than the soaking treatment. In general, high yields were achieved by early planting of seeds and minimum root rot.