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  • Author or Editor: Kent J. Bradford x
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Abstract

Waterlogging of the soil rapidly and dramatically alters both the physical and biological environment of plant roots. In response to environmental stimuli, physiological events occur within the plant which affect its growth and development. The purpose of this paper is to review certain aspects of the physiological responses of plants to waterlogging with respect to the response mechanisms and the subsequent adaptations in the growth and development of the whole plant. Many important aspects of the subject must be only briefly mentioned here, such as the effects of waterlogging on soil chemistry, nutrient availability and uptake, microbiology, pathology, and senescence. The reader is referred to recent literature for information on these topics (3, 13, 19, 21). The overriding effect of soil flooding is to limit the diffusion of oxygen to the root zone. The focus here, therefore, will be on the responses of plants to root anaerobiosis and some initial, rapid mechanisms of adjustment. Further information on long-term adaptation, especially in woody plants, can be found elsewhere (76).

Open Access

Abstract

Plants of two cultivars of processing tomato (Lycopersicon esculentum Mill, cvs. UC82B and VF145B-7879) were sprayed with ethephon solutions 10 days prior to harvest. Seeds were extracted from fruits that had been tagged at anthesis to allow separation into age classes ranging from 31 to 70 days at harvest. Seed dry weight increased rapidly until ≈40 days after anthesis, then remained relatively constant for 10 to 15 days before increasing again. During the plateau phase, the initial (5-day) germination percentages increased by 20% to 40% and final (10-day) germination increased by 6% to 10%. Germination percentages then fell slightly with increasing maturity and dry weight accumulation. Preharvest ethephon treatment caused younger fruit to ripen and shifted the development of maximum germinability toward young seed ages, without influencing dry weight accumulation. Seeds ≤53 days old at harvest increased in germination due to ethephon treatment, whereas seeds older than 53 days showed decreased germination. Since the bulk of harvested seeds will be in the older classes, overall seed quality may be affected adversely by preharvest ethephon applications. Although seed lots from ethephon-treated plants still had acceptable germination, there would appear to be no benefit from ethephon applications to tomatoes destined solely for seed production. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon).

Open Access

Abstract

Ag(I), applied in aqueous solution as AgNO3, inhibited ethylene synthesis and ripening of mature green banana fruit slices and pericarp discs of mature green tomato fruit. It also inhibited ethylene production by cortical tissue from post-climacteric apples. Concentrations of Ag(I) which reduced ethylene synthesis had an inconsistent effect on CO2 production: no effect on banana slices (1.0 mm Ag+), stimulation in apple tissue (0.1 mm Ag+), and inhibition in tomato tissue (0.3 mm Ag+). This was accompanied by a slight amount of tissue necrosis at these concentrations. Of the 7 metallic salts tested, only Ag(I) inhibited ripening and ethylene synthesis at observed non-phytotoxic levels. Inhibition of ripening and ethylene synthesis by Ag(I) was evident in tissue treated with sufficient exogenous ethylene to elicit both responses in control tissue. The inability of applied ethylene to overcome the inhibitory effect of Ag(I) suggests that the silver ion may interfere with the primary action of ethylene in the tissue.

Open Access

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.

Open Access

Abstract

Osmotic priming of seed was evaluated as a means of improving stand establishment, early seedling growth, and yield of processing tomatoes (Lycopersicon esculentum Mill. cvs. UC204 and 6203). Seeds were primed in aerated solutions of 3% KNO3 (w/v) or of polyethylene glycol 8000 (PEG) of equivalent osmotic potential (-1.25 MPa; 314 g-kg−1 of water) at 20°C for 7 days, rinsed, and dried in forced air at 30°. Under laboratory conditions, seeds primed in either osmoticum germinated more rapidly than untreated seeds at 20° and 30°. At 10°, the PEG treatment was of little benefit for either variety, while the KN03 treatment still reduced the time to 50% germination to 60% to 80% of the control value. Priming did not affect the final germination percentage. Seedling emergence in the field was evaluated in March and April planting dates. In both trials, seedlings from primed seeds emerged earlier and more uniformly than seedlings from untreated seeds. Seedlings from primed seeds maintained greater mean plant dry weights, leaf areas, and ground cover percentages than untreated seedlings throughout the preflowering period. This advantage was due entirely to early emergence rather than to an increased relative growth rate. The early growth advantage from seed priming did not improve earliness of maturity, total yield, or soluble solids content of fruit.

Open Access

While seed priming (hydration in water or osmotic solutions followed by drying) enhances seed germination performance, the longevity of primed seeds in storage often is reduced. Postpriming treatments including a reduction in seed water content followed by incubation at 37 or 40 °C for 2 to 4 h can substantially restore potential longevity in tomato (Lycopersicon esculentum Mill.) seeds. These conditions might induce heat-shock proteins (hsp) that could be involved in the extension of seed longevity. The abundance of BiP (78 kD Binding Protein), hsp70 and class I small hsp in primed seeds subjected to postpriming treatments was examined to assess this possibility. BiP mRNA and protein amounts increased during postpriming heat treatments that extended longevity of tomato seeds. Treatment of primed seeds with the calcium ionophore calcimycin (A21387) enhanced BiP protein accumulation in the absence of heat treatment and also extended potential seed longevity. Changes in the abundance of hsp70 and class I small hsps were not consistently associated with potential seed longevity. Thus, enhanced BiP expression may contribute to the improved longevity of primed seeds following postpriming treatments.

Free access

Abstract

Lettuce (Lactuca sativa L. ‘Empire’) seeds (achenes) were given an osmotic priming treatment (24 hr in aerated —1.5 MPa polyethylene glycol (PEG 8000) solution at 18°C in the light) which alleviated thermodormancy in laboratory tests. The seeds then were coated commercially for precision planting. Additional seeds also received a proprietary treatment for enhancing high temperature germination (Royal Sluis Split-kote D). In field trials in the Imperial Valley of California, where the soil temperature exceeded 35°C for the first 11 hr of imbibition under sprinkler irrigation, total emergence of untreated seeds after 6 days was between 18% and 21%, whereas that of primed and Splitkote D seeds ranged from 46% to 69%. Uniformity and rate of emergence were also greater for the primed seeds, with 91 % of the final emergence occurring by the 3rd day, as compared to only 70% for the control. Seed priming prior to coating can be an effective method of improving lettuce stand establishment under high temperature conditions.

Open Access

The interactions of seed vigor with herbicides were studied with respect to seedling emergence, growth, and fruit yield of processing tomatoes (Lycopersicon esculentum Mill. cv. UC204C). Seed vigor (speed of germination) was enhanced by priming in an aerated solution of 0.12 m K2HP O4 plus 0.15 m KN O3 at 20C for 5 days followed by drying in forced air at 30C. The vigor of a second subsample of the same seed lot was reduced by controlled deterioration at 13% water content (dry-weight basis) for 6 days at 50C (aged seeds). Primed, aged, and untreated seeds were tested for their sensitivity to napropamide and metribuzin herbicides in greenhouse and field studies. A seed vigor × herbicide interaction was detected only under greenhouse conditions, where aged seeds were more sensitive than primed or untreated seeds to metribuzin. In April and May field plantings, seed vigor influenced the rate and percentage of final emergence and the earliness of fruit maturity, but had no effect on relative growth rate or total vegetative or reproductive yield. Napropamide at 4.5 and 9 kg·ha-1 and metribuzin at 0.4 and 0.8 kg·ha-1 had no effect on the rate or percentage of seedling emergence, relative growth rate, or total fruit yield. Metribuzin increased the mortality of seedlings at either application rate, and at 0.8 kg·ha-1 delayed early growth and fruit maturity in the April planting. Napropamide treatments did not differ from the water control for all characteristics and environments studied. Chemical names used: 4-amino-6-tert-butyl-3(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin); 2-(α-napthoxy)-N,N-diethyl propionamide (napropamide).

Free access

Agricultural producers in the United States require timely and accurate information on critical issues, environmental crises, and best management practices to make effective production decisions and to remain competitive in a global economy. Sources of information (university departments, extension, industry, consultants, scientific and trade publications) often take a single discipline approach that makes it difficult for growers to process and utilize information effectively. The high cost of printed publications make frequent updates impractical, while rapidly changing technologies and issues demand continual publication changes and updates. The rapid development and peer review of multi-discipline, research based information is possible through computer information transfer technology. The Univ. of California's Vegetable Crops Research and Information Center (VRIC) has developed a new World Wide Web site to disseminate peer-reviewed fact sheets, research results, updated publications, and multi-media educational resources relating to critical issues, best management practices, postharvest handling, and marketing of vegetable crops. The website disseminates multi-discipline information originating from the Univ. of California, the USDA, and cooperating agencies and universities. The VRIC website proactively sends peer-reviewed critical issue fact sheets to selected news media, government, industry, and academic contacts. These fact sheets help personnel frequently contacted by the media during crises to answer questions effectively. The website directs visitors to additional agricultural information resources and contains information on careers and educational opportunities available in the field of vegetable crops.

Free access

A seedling disorder of broccoli (Brassica oleraceae L. var. italica) characterized by chlorotic cotyledons and delayed seedling growth is described. This disorder, termed “yellow cotyledon”, has been observed in field plantings under high temperatures with some broccoli seed lots. Yellow-cotyledon disorder can be observed in laboratory germination tests if they are conducted under illumination, where unaffected seedlings will develop green cotyledons. Little relationship was found between overall seed vigor and the expression of yellow cotyledon by use of early germination counts and accelerated aging tests, although the most severely affected seed lots had been stored for several years. Field trials in 2 years showed that although seedlings with yellow-cotyledon disorder developed into normal plants, maturity was delayed and total yields were reduced.

Free access