Search Results
Abstract
There are relatively few references dealing with the role of man as a virus vector, and none that is so specific as to examine the role of plant breeders in the dissemination of virus diseases. Therefore, I have relied to a large extent on unpublished observations and what I hope is an unbiased interpretation of some selected papers on plant virus epidemiology. Some statements may appear outrageous initially. The following sentence is provocative: “Plant breeders usually possess only a superficial knowledge of plant viruses and the mechanisms by which they are transmitted.” This statement is not intended to belittle the training or competence of plant breeders. It is simply what I consider to be a statement of fact. Further, I suspect it will continue to be true for the foreseeable future. It would be equally true if the statement were reversed: “Plant virologists usually possess only a superficial knowledge of plant breeding and the mechanisms by which genetic factors are transmitted”.
Fertilization is the most expensive cultural practice for the increasing numbers of organic vegetable growers in the United States. Nitrogen (N) is the most important and costly nutrient to manage, and cost-effective N management practices are needed for efficient organic vegetable production. There is a wide array of organic N sources available, but they vary in cost, N content, and N availability. Compost and cover crops are commonly used sources of N for vegetables because they are relatively inexpensive and offer additional nutrients or soil improvement qualities in addition to N. Studies have shown that compost quality factors that affect N mineralization vary by source and among different batches from the same source. Compost carbon to N ratio should be equal to or less than 20:1 to assure net short-term mineralization. Cover crops also vary in N content and mineralization rate after incorporation. Leguminous cover crops decompose and release N more rapidly than grass or cereal cover crops at the preheading stage typically incorporated. Even the most efficient N-supplying composts, cover crops, or other organic N sources do not release appreciable N to a subsequent crop beyond 6 to 8 weeks from incorporation, and this burst of early N may not synchronize with N requirements for many vegetable crops. Other potential organic fertilizer N sources have been evaluated for vegetables, and they vary in N cost and N mineralization rate. Materials evaluated include seabird guano, liquid fish, feather meal, corn meal (Zea mays), blood meal, and liquid soybean meal (Glycine max) among others. Of those evaluated, feather meal, seabird guano, and liquid fish stand out as more economical organic sources of available N. Organic sources generally lack uniformity and are bulky, unstable, and inconsistent as a group, and this contributes to additional hidden management costs for organic growers. Liquid organic N sources for use in microirrigation systems may have additional disadvantages caused by loss of valuable nutrient N that is removed by filters.
Abstract
Mechanically harvested fruit of the strawberry (Fragaria × ananassa Duch.) cv. Veeglow destined for processing can be stored at 1°C in bulk bins for 4 to 6 days if room-cooled, and for 6 to 8 days if forced-air cooled promptly after harvest, without appreciable loss due to rot development or of quality of processed product. Yields of puree from fresh fruit mechanically harvested on day 8 of the storage trial were lower than for fruit that had been forced-air cooled and stored at 0° for 8 days. Sulfur dioxide fumigation immediately after cooling reduced losses due to rot and lowered mold counts, particularly when the fruit was room cooled.
Strawberries (Fragaria × ananassa Duch.) cv. Redcoat were stored at several temperatures and for various intervals in controlled atmospheres (CA) containing 0% to 18% CO2 and 15% to 21% 02. Bioyield point forces recorded on the CA-stored fresh fruit indicated that the addition of CO2 to the storage environment enhanced fruit firmness. Fruit kept under 15% CO2 for 18 hours was 48% firmer than untreated samples were initially. Response to increasing CO2 concentrations was linear. There was no response to changing 02 concentrations. Maximum enhancement of firmness was achieved at a fruit temperature of 0C; there was essentially no enhancement at 21C. In some instances, there was a moderate firmness enhancement as time in storage increased. Carbon dioxide acted to reduce the quantity of fruit lost due to rot. Fruit that was soft and bruised after harvest became drier and firmer in a CO2-enriched environment.
Abstract
Multiple linear regression analysis was used to develop commercial harvest prediction dates for peach ‘Earlired’, ‘Redhaven’, and ‘Loring’. Prediction equations were developed using degree day summations and date of full bloom as variables. These equations were adjusted for geographic microclimatic variation and tested in 6 commercial peach orchards over 4 years. Predicted dates and actual first commercial harvest dates differed by 4 days or less for 100%, 96%, and 84% of the predictions for ‘Earlired’, ‘Redhaven’, and ‘Loring’, respectively.
In recent years, vegetable growers on the central coast of California have come under increasing regulatory pressure to improve nutrient management and reduce nitrate losses to ground and surface waters. To achieve this goal, growers must understand the nutrient uptake and water use characteristics of their crops. For fresh market spinach (Spinacia oleracea), production methods and cultivars have greatly changed in the last 10–15 years, and as a result, few publications are available on nutrient uptake by modern spinach production methods. This study evaluated nutrient uptake and water use by spinach to provide strategies to better manage nitrogen (N) fertilizer and irrigation applications. In 2011, four fertilizer trials and a survey of 11 commercial fields of spinach grown on high-density plantings on 80-inch beds were conducted on the central coast of California. During the first 2 weeks of the crop cycle, N, phosphorus (P), and potassium (K) uptake was 7.0, 0.6, and 7.2 lb/acre, respectively. In the subsequent 2–3 weeks before harvest the N, P, and K uptake rate was linear and was 4.3, 0.6, and 7.8 lb/acre per day, respectively. N uptake at harvest for the three commercial size categories baby, teenage, and bunch was 74, 91, and 120 lb/acre N, respectively. Of the N in aboveground biomass at harvest, 41% was left in the field following mechanical or hand harvest. Growers at 14 of 15 study sites applied on average 111% more N than was taken up in aboveground biomass at harvest. Results from four fertility trials showed that first crops of the season had low initial soil nitrate concentrations (≤10 ppm), and an at-planting fertilizer application was necessary for maximum yields. For fields following a previous crop (second- or third-cropped) with initial soil nitrate concentrations >20 ppm, at-planting and midseason fertilizer applications could be greatly reduced or eliminated without jeopardizing yield. Rooting depth and density evaluations at four sites showed that 95% of roots were located in the top 16 inches of soil at harvest. To mitigate environmentally negative N losses, the N use efficiency (NUE) can be increased by the use of soil testing done at two critical time points: at-planting and before the first midseason fertilizer application.
High levels of residual soil nitrate are typically present in cool-season vegetable fields in coastal regions of California in the fall, after the production of multiple crops over the course of the growing season. This nitrate is subject to leaching with winter rains when fields are left fallow. Although the benefits of growing nitrate scavenging cover crops on soil and water quality are well documented, the portion of vegetable production fields planted to winter cover crops in this region is low. Most growers leave their fields unplanted in bare-fallow beds because the risk of having too much cover crop residue to incorporate may delay late winter and early spring planting schedules. A possible strategy to derive benefits of a cover crop yet minimize the amount of residue is to kill the cover crop with an herbicide when biomass of the cover crop is still relatively low. To evaluate whether this strategy would be effective at reducing nitrate leaching, we conducted field studies in Winter 2010–11 (Year 1) and Winter 2011–12 (Year 2) with cereal rye (Secale cereale). Each trial consisted of three treatments: 1) Fallow (bare fallow), 2) Full-season (cover crop allowed to grow to full term), and 3) Partial-season (cover crop killed with herbicide 8 to 9 weeks after emergence). In Year 1, which received 35% more rainfall than the historical average during the trial, the Full-season cover crop reduced nitrate leaching by 64% relative to Fallow, but the Partial-season had no effect relative to Fallow. In Year 2, which received 47% less rainfall than the historical average during the trial, the Full- and Partial-season cover crops reduced nitrate leaching by 75% and 52%, respectively, relative to Fallow. The Full-season cover crop was able to reduce nitrate leaching regardless of yearly variations in the timing and amount of precipitation. Although the Partial-season cover crop was able to reduce leaching in Year 2, the value of this winter-kill strategy to reduce nitrate leaching is limited by the need to kill the crop when relatively young, resulting in the release of nitrogen (N) from decaying residues back into the soil where it is subject to leaching.
Pepper stip is a physiological disorder manifested as gray-brown to greenish spots occurring on the fruit of bell, pimento, Anaheim, and other types of peppers, most noticeably on red fruit that mature under fall conditions. Most hybrid bell cultivars are resistant to the malady; the problem is most severe for pepper growers reliant on less-expensive, open-pollinated cultivars. In 1995, we initiated studies to evaluate the possible link between mineral nutrition and this disorder. Two susceptible open-pollinated cultivars and two resistant hybrid cultivars were grown in randomized plots at seven sites. Significant correlations were seen between the levels of potassium (r = 0.59) and calcium (r = -0.37) in whole leaves and the incidence of stip (P = 0.05). The stip-resistant cultivars also maintained less total nitrogen in the whole leaves than susceptible cultivars (P = 0.05). In 1996 and 1997, we undertook field studies to evaluate the effects of varying calcium and nitrogen application rates. Inconsistent results were observed with calcium applications. Moderate reductions in stip incidence was observed at some sites and no reduction at others following foliar calcium applications. Nitrogen nutrition had no effect on stip severity. In 1998, evaluation of a large number of open-pollinated cultivars was undertaken; `Gusto' showed excellent tolerance to pepper stip, followed by `Taurus' and `Cal Wonder 300'. We conclude that growers that are reliant on open-pollinated cultivars can utilize these cultivars to minimize the incidence of pepper stip.
Pepper stip is a physiological disorder manifested as gray-brown to greenish spots occurring on fruit of bell, pimento, Anaheim, and other types of peppers, most noticeably on red fruit produced under fall conditions. The spots, ≈0.5 cm in diameter, occur singly or in groups; marketability for either fresh market or processing use is severely affected. The factors controlling the occurrence or severity of the disorder are not well understood; to date, control has been achieved primarily by the use of resistant cultivars. In 1995 replicated plots of susceptible (`Yolo Wonder L' and `Grande Rio') and resistant (`Galaxy' and `King Arthur') cultivars were grown in seven commercial fields in central California. `Galaxy' and `King Arthur' were essentially free of symptoms, while `Yolo Wonder L' and `Grande Rio' showed significant damage at all sites, with 23% to 88% of fruits affected at the mature-red stage. Petiole tissue analysis showed that resistant cultivars consistently had lower N and K, and higher Ca concentrations than susceptible cultivars; the same trend was apparent in fruit tissue. Stip was most severe at sites with low soil Ca and/or very high N and K fertilization rates. It is hypothesized that Ca nutrition significantly influences stip expression.
Abstract
Celery (Apium graveolens L. var. dulce DC.) stored at 0°-1°C in 1.5% O2 had better marketable quality than that stored in air after 11 weeks. Marketable celery was improved by using 2.5-7.5% CO in the storage atmosphere, but not by 2-4% CO2. Decay was most severe on celery stored in 21% O2. Botrytis cinerea Pers. and Sclerotinia sclerotiorum (Lib.) de Bary were the most frequent isolates recovered from decayed celery.