Concentrations of selenium (Se) in agricultural irrigation effluent increased stored soil Se to toxic levels in the wetland sediment at Kesterson Reservoir. Vegetation management (phytoremediation) may be a strategy to reduce these soil Se concentrations to nontoxic levels. Selenium in plant shoots and depletion of soil Se removal by selected plant species were evaluated over a 1‐yr period under greenhouse conditions. Two soils were used: a seleniferous Turlock soil (collected from Kesterson Reservoir) that contained high total Se (∼40 mg kg−1 soil), high water extractable B (∼10 mg B L−1), a soil salinity of ∼8 dS m−1, and a nonseleniferous Hanford sandy loam (collected from an agricultural field site). Three plant species tested were Brassica napus cv. Westar (canola), Hibiscus cannabinus L. cv. Indian (kenaf), and Festuca arundinacea Schreb. cv. Alta (tall fescue). Only canola and kenaf grown in Turlock soil showed significant lower shoot yield (P < 0.01) than on the Hanford soil. Leaf Se was as high as 470 mg Se kg−1 DM in canola, 45 mg Se kg−1 DM in kenaf and 50 mg Se kg−1 DM in tall fescue. The same crops contained mean leaf B concentrations as high as 415 mg B kg−1 DM in kenaf, 180 mg B kg−1 DM in canola, and 111 mg B kg−1 DM in first clipping of tall fescue. The cultivation of all species led to a significant reduction (P < 0.01) of total soil Se between preplant and the final harvest by the following percentages: canola (47%), kenaf (23%), and tall fescue (21%). Successively planting of canola and to a lesser extent kenaf and tall fescue, in Se‐laden soil has the potential to reduce total soil Se.
The southern root‐knot nematode, Meloidogyne incognita race 3 (Kofoid & White) Chitwood, and the reniform nematode, Rotylenchulus reniformis Linford & Oliveira, are the most widespread and economically important nematode pests of Upland cotton (Gossypium hirsutum L.) and Pima cotton (G. barbadense L.) in the USA. Progress in the development of nematode‐resistant cotton cultivars is unclear. Plant breeders often have selected for nematode tolerance by measuring cotton yield in nematode‐infested fields but seldom have selected for resistance by measuring nematode reproduction. The objective of this research was to measure nematode reproduction to assess progress in the development of nematode resistance in cotton. Fiftyfive Upland and four Pima cotton cultivars, comprising the most widely planted cultivars in the USA each decade since 1950, were evaluated in growth chambers for resistance to M. incognita and R. reniformis. The cultivar Deltapine 16 served as the susceptible and the germplasm line Auburn 623 RNR as the resistant control. Reproduction by M. incognita on the cultivars ranged from 4 to 294% of that on Deltapine 16. All cultivars were highly susceptible to R. reniformis. A small increase was detected in the general level of resistance to M. incognita between 1950 and 1996, but only the recently released cultivars, Stoneville ‘LA887’, Paymaster ‘1560’, and CPCSD ‘Acala Nem‐X’, showed consistently high resistance. These cultivars were developed by measuring nematode reproduction in pots or root galling in field plantings, as well as yield and related agronomic traits.
Root growth and distribution are important plant adaptations to conditions where limited soil water availability is a major constraint to crop growth and yield. Field studies were conducted to evaluate root characteristics at seedling stage and first bloom of six cotton (Gossypium hirsutum L.) genotypes, and to determine the relationship between root growth parameters and drought‐influenced boll abscission and lint yield. Genotypes included in the studies were: Tamcot SP37H (SP37H), Tamcot CD3H (CD3H), TX‐CABUCS‐2‐1‐83 (CABUCS), TX.MACAOS‐3‐84 (MACAOS), Paymaster 303 (PAY303), and Deltapine 41 (DPL41). Significant differences occurred between genotypes for seedling and first‐bloom plant measurements, with CD3H and CABUCS having higher levels of seedling vigor, more rapid root system establishment and lower root‐to‐shoot ratios. Regression analyses indicated a positive association (R2 = 0.47, P < 0.01) between drought‐induced boll abscission and root‐to‐shoot ratio at first bloom, while a negative relationship (R2 = 0.30, P < 0.01) was observed between dryland lint yield and first‐bloom root‐to‐shoot ratio. Results suggest that selection for and incorporation of increased seedling vigor, rapid root‐system establishment and lower root‐to‐shoot ratios into future cotton germplasm could improve drought tolerance and lint yields in regions subjected to limited or poorly distributed rainfall conditions.
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