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program and to identify which viroids occur in Texas. Biological indexing, the gold standard in virus-free citrus production, is expensive, time-consuming but a necessity ( Skaria et al., 1997 ). However, there may be potential for a conditional

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improve fruit visual, nutritional, and flavor quality. The identification of nutrient deficiency symptoms is relatively complex, due to the various biological functions and interactions that occur between nutrients and the environment, and even similar

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Abstract

Carrot (Daucus carota L. cv. Danvers) seed were produced at plant spacings of 0.05, 0.10, 0.20, and 0.30 m in 0.80-m rows to give populations of 25, 13, 6, and 4 plants/m2. Samples from the adjacent commercial carrot seed field provided an additional density of 36 plants/m2. Seed yield, harvest index, and seed quality were evaluated with respect to umbel order and plant density. Phenological development was unaffected by plant density, but plant height increased significantly as density increased. The number of umbels per plant and the number of seeds per umbel decreased with increasing plant density, while seed weight was unaffected. The proportion of the seed contributed by primary umbels increased from 20% at the lowest to 60% at the highest density. Seed yield per plant declined continuously as population increased, but seed yield per unit area increased to a maximum at 12 plants/m2, then declined. Total biological yield (above-ground biomass) rose to a plateau level with increasing plant population. Ceiling biological yield coincided with maximum seed yield. Seed quality within each umbel order, assessed by germination percentage and rate, seedling growth, embryo length, and abnormal or embryoless seeds, was unaffected by plant density, but consistently decreased from primary to tertiary umbel orders. Harvest index (seed yield/biological yield) was highly correlated with seed quality. The relationship between harvest index and plant density in carrot seed production may be useful in optimizing plant populations for maximum seed yield and quality.

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biological diversity, which may impact P cycling and P uptake by crops. Increases in organic matter will be accompanied by increases in organic P. Management of cover crops and potentially enhanced AMF colonization can increase the availability of soil P pool

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Bruce Ames and associates have generated a HERP (Human Exposure/Rodent Potency) index that is useful for putting relative carcinogenicities in perspective. His data can be made more useful by translating to a common denominator, as has been done in the BURP (Better Understanding of Relative Potencies) index, showing. for example, that a liter of wine is 18,000 times more carcinogenic (for the ethanol) than a liter of chlorinated water (for the chloroform). For the ethanol. 1 liter of beer is 8000 times; for formaldehyde, 1 liter of kola is 7700 times; for the safrole, 1 liter of old-fashioned root beer is 575 times; for symphytine, 1 liter of comfrey leaf tea is 125 times; and, for the unsymmetrical dimethylhydrazide (UMDH), 1 liter of apple juice is only 10 times as carcinogenic as 1 liter of tapwater. In the FNF (Father Nature's Fannacy) database, biologically active compounds in plant foods are quantified (parts per million). Where available, LD50s. ED50s, and ID50s of these biologically active compounds are incorporated to index, respectively, relative acute toxicities, effective doses, and inhibitory concentrations. in indices that parallel the HERP and BURP indices.

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Abstract

Two lines of black bean (Phaseolus vulgaris L.), ‘70001’ and ‘Strain 39’, were grown at between-row spacings of 76, 61, and 46 cm. Cultivation treatments included an uncultivated check and a single cultivation at 1 of 3 plant growth stages: first trifoliolate leaf fully expanded; anthesis; or pod elongation. Root weight, shoot weight, and shoot:root ratio of individual plants decreased linearly as between-row spacing decreased. Biological yield increased linearly as between-row spacing decreased, but seed yield and harvest index did not show significant responses to spacing. None of the measured parameters gave a significant response when the uncultivated control was compared with the average of the 3 time-of-cultivation treatments. Root weight of individual plants and biological yield gave quadratic responses within the 3 time-of-cultivation treatments, both decreasing most markedly with cultivation at the pod elongation stage. Plants of ‘70001’ were larger and lodged less compared to those of ‘Strain 39’. Seed yields of both lines were similar. Results suggest that a single shallow cultivation may be used for black beans grown in narrow rows through anthesis. Although cultivation at the pod elongation stage was generally not detrimental to seed yield, it is not recommended.

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To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short and medium term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Methods for the measurement of plant water potential (Ψ) are available, but conflicting results have led to disagreement as to whether any of these give an appropriate biological index of plant water stress. Some pressure chamber results may be attributed to an artifact of water loss following excision. Leaf and stem Ψ however, in addition to being numerically different, may not be equivalent indices of plant stress, and midday stem Ψ has proven to be a useful index of stress in a number of fruit trees. Day to day fluctuations in midday stem Ψ under well irrigated conditions is well correlated to midday Vapor Pressure Deficit, and hence can be used to predict a non-stressed baseline. A 50% decline in water use at both the leaf and canopy level were associated with relatively small reductions (0.5 to 0.6 MPa) in midday stem Ψ from this baseline in prune. In cherry, midday stem Ψ was correlated to both leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once midday stem Ψ dropped to between -1.5 to -1.7 MPa. In pear, increased fruit size, decreased fruit soluble solids and increased green color were all associated with increases in midday stem Ψ.

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Field experiments with 15 sweet potato [Ipomoea batatas L. (Lam.)] genotypes were conducted to study the physiological basis of yield in 1981 and 1982. The leaf area index differed significantly among the sweet potato genotypes during early and late phases of growth, hut showed an inconsistent relationship with yield. Single leaf net photosynthesis ranged from 0.74 to 1.12 mg CO2/m' per sec. Canopy photosynthesis for sweet potato genotypes differed significantly in 1981, but not in 1982. It ranged from 0.81 to 1.16 mg CO2/m2 per sec in Aug. 1981. and from 0.63 to 0.88 mg CO2/m2 per sec in 1982. Four hours after “C-labeling, 14C-assimilate translocation from the treated leaf ranged from 21% to 46%, but did not differ significantly among the genotypes. At final harvest, harvest index [HI, defined as (storage root yield/total biological yield) × 100] of the genotypes varied from 43% to 77% and 31% to 75% for 1981 and 1982, respectively. Canopy photosynthesis during September was significantly correlated with storage root dry matter yield (r = 0.54*) in 1981 and with phytomass (above-ground biomass plus storage roots) (r = 0.60*) in 1982. Both phytomass and HI were significantly correlated with storage root matter yield. Canopy photosynthetic evaluation of sweet potato germplasm may be-more relevant when the storage root sinks are at an advanced stage of development. Our study suggests that yield is poorly predicted by Pn, particularly when the genotypes have different leaf sizes.

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The herbicides paraquat, trifluralin, and metolachlor were compared for efficacy of weed control in cowpea [Vigna unguiculata (L.) Walp.] with and without cultivation as a supplemental strategy. Herbicides also were compared against a no cultivation-no herbicide treatment (control) and against cultivation without an herbicide. Cultivation had no significant effect on seed yield, biological yield, or harvest index of cowpea. Paraquat, applied before seeding but after emergence of weeds, was ineffective for weed control and usually did not change cowpea yield from that obtained without an herbicide. Trifluralin and metolachlor more than tripled cowpea seed yield compared with that obtained without an herbicide in 1988, when potential weed pressure was 886 g·m-2 (dry weight). The main effects of trifluralin and metolachlor were not significant for cowpea seed yield in 1989, when potential weed pressure was 319 g·m-2 (dry weight). However, in 1989, these two herbicides still increased cowpea seed yield compared with that of the control and increased net farm income by more than $300/ha compared with the income obtained from the control. Chemical names used 1,1'-dimethyl-4,4' -bipyridlnium salts (paraquat); 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine (trifluralin); 2-chloro-N-(2-ethyl-6 -methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide (metolachlor).

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The herbicides trifluralin, metolachlor, and paraquat were compared for efficacy of weed control in cowpea with and without cultivation as a supplemental strategy for two years. Herbicides also were compared against a no-herbicide control (with and without cultivation). Cultivation had no significant effect on seed yield, biological yield, or harvest index of cowpea. Paraquat, used in a “stale seedbed” system, was ineffective for weed control and did not change cowpea yield from that of the no-herbicide control. Trifluralin and metolachlor more then tripled cowpea seed yield compared to that of the no-herbicide control in 1988, when potential weed pressure was 886 g m-2 (dry wt.). Trifluralin and metolachlor did not significantly increase cowpea seed yield compared to that of the no-herbicide control in 1989, when potential weed pressure was 319 g m-2 (dry wt.). However, in 1989, these two herbicides each still increased net farm income by $206 per hectare compared to the income obtained without an herbicide.

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