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.
Richard Smith, Bob Mullen, and Tim Hartz
R.P. Flynn, C.W. Wood, and E.A. Guertal
A glasshouse study was conducted to evaluate the suitability of composted broiler chicken (Gallus gallus) litter as a potting substrate using lettuce (Lactuca sativa L.). Broiler litters containing wood shavings or peanut bulls as bedding materials were composted with either shredded pine bark or peanut hulls. Composted materials were then combined with a commercially available potting substrate. Greatest fresh weight yield was obtained when peanut bull compost was mixed with commercial potting substrate at a ratio of 3:1. Fresh weight was less with pine bark compost than with peanut hull compost. However, there were no differences in lettuce dry weight among composts except for pine bark composted with wood-shaving broiler litter. The pH of this material was below the lettuce tolerance level for mixes at or above 50% compost. There was no evidence of lettuce physiological disorders resulting from excessive nutrient concentration. Most elements analyzed (N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, and Al) were within or slightly above sufficiency ranges for Boston-type leaf lettuce. It appears that composting broiler litter for use as a potting substrate or component would be one suitable alternative to land application in the southern United States. We recommend, however, that the pH of substrates be adjusted to suit desired crop requirements.
Esmaeil Fallahi and Thomas Eichert
Foliar fertilization is a common practice to supply crops with mineral nutrients, especially under limited soil nutrient availability conditions. However, foliar-applied nutrients have to overcome the barrier properties of leaf surface to be absorbed by plants. Various pathways are reported to explain the penetration of foliar nutrients through the leaf tissues. Meanwhile, we believe that air humidity is one of the main controlling factors in this process since it controls both the actual nutrient concentration on the leaf surface as the driving force of absorption and the permeability of the leaf surface. Postharvest and prebloom foliar nitrogen sprays are applied to enhance flower bud vigor, and calcium (Ca) is applied directly to fruit during the growing season to reduce fruit susceptibility to physiological disorders. Micronutrients typically are applied in foliar sprays to uniformly distribute the small quantities of these required nutrients. In this report, we focus on the principles of foliar nutrient uptake and impacts of foliar urea and Ca sprays on fruit quality attributes of ‘Fuji’ apples (Malus domestica). Based on our studies, a ground application of urea is critical for a higher production of ‘Fuji’ apple.
Richard Smith, Robert Mullen, and Tim Hartz
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.
Christopher Gunter, David Francis, and Alba Clivati McIntyre
Yellow shoulder disorder (YSD) is a physiological disorder of processing tomato that affects both the appearance and nutritional quality of the fruit. This disorder reduces the suitability of fruit intended for the whole-peeled and diced product markets. The YSD involves an interaction between plant genotype and the environment. A number of soil factors have been related to the incidence of YSD, including organic matter, phosphorous, K/Mg ratios, and soil K. Varieties of tomatoes differ in their susceptibility to color disorders, thus variety selection offers growers one strategy to manage this color disorder. The use of supplemental K application at a time when plants are blooming and actively growing offers a second strategy for management of YSD. To this end, a field study was conducted at the Southwest Purdue Agricultural Program in southwestern Indiana to study the effects of different sources of K on the color and quality of tomato fruit. Potassium chloride, potassium nitrate, and potassium sulfate were applied at first flowering in a solid, broadcast application. Appropriate controls were used to balance the nutrients supplied in addition to K. Supplemental K, regardless of source, improved fruit hue, though the trend was not always statistically significant between treatments. Variety specific effects were observed. This is a complex disorder and its management will entail minimizing risk of incidence through careful selection of variety and field location.
Robert F. Bevacqua
Cork spot is a serious physiological disorder in pear (Pyrus communis L. cv. d'Anjou) in the United States, but a reliable technique for diagnosing it has not been developed. A review of the scientific literature indicated the disorder was generally linked with low calcium concentration in the fruit. In the present study, mineral analyses were conducted in 1987 and 1988 on soil, leaves, and fruit peel from normal trees and trees prone to cork spot. Soil tests and leaf analysis did not provide measureable differences between the two groups of trees. Fruit analysis provided variable differences between normal and cork spotted fruit, but no single nutrient or ration of nutrients could be consistently associated with the disorder. An assay for pyruvate kinase was evaluated as a diagnostic tool for cork spot. The assay did not provide measureable differences between normal and cork spotted fruit. An important finding of this study was to learn cork spotted fruit had higher soluble protein concentration than normal fruit.
John Navazio and Jack E. Staub
A fruit anomaly, pillowy (P), has been identified in processing cucumber This physiological disorder has been shown to be accelerated by water stress.
A series of experiments were conducted to determine postharvest handling procedures which minimize the appearance of pillowy after induction by water stress. Isogenic lines evaluated in RCB design with 3 replications where subjected to water stress during fruit enlargement. Fruits were then subjected to various storage temperatures and times before hydrocooling to 8°C. Cucumbers were then fresh pack processed and evaluated for % pillowy after 12 weeks,
The postharvest control treatmcnt (2 days, 26°C, 60% RH) produced 32%P to 51%P in fruit subjected to stress and 23%P to 39%P in unstressed fruit. In the optimal postharvest treatment (1 day, 26°C, 60% RH, then hydrocool to 8°C, 2 days, 15°C, 85% RH) fruits from stress plants exhibited 23%P to 39%P and those from nonstress plants showed 13%P to 26%P. Fruits from miniature leaf lines exhibited higher percent (37%) P ratings when compared to normal leaf lines.
V.H. Escalona, E. Aguayo, and F. Artés
Fresh-cut diced (1 cm3) kohlrabi (Brassica oleracea L. Gongylodes Group) `Kompliment F1' washed with chlorinated (100 mg·L-1) water was stored in modified atmosphere packaging (MAP) up to 14 days at 0 °C. Samples were packed in 35-μm oriented polypropylene (PP) bags or in plastic trays heat-sealed with unperforated or perforated (control) PP film. Changes in respiratory rate, ethylene emission rate, microbial growth, color, browning, decay, sugar contents, chemical attributes (soluble solids content, pH, and titratable acidity), and sensory attributes (visual appearance, aroma, flavor, and texture) were monitored. Cutting resulted in an increased CO2 production compared to the whole stem, ranging from 2-fold immediately after cutting, to 8-fold at day 4. The equilibrium atmospheres within bags and trays were 6% O2 plus 13% CO2, and 13% O2 plus 8% to 9% CO2, respectively. In both MAP treatments, microbial development was delayed compared to air (control). The total aerobic counts were lower than 7.7 log CFU/g, which has been defined as are commended limit criteria. No physiological disorders, decay. or off-flavor developed. Therefore, sensory quality attributes were suitable for commercial purposes. However, fresh-cut kohlrabi stored in MAP had slightly better color retention and microbial quality than the control.
Jorge B. Retamales and Claudio Valdes
Bitter pit is the most important physiological disorders for apples in Chile. During the 1995–96 season, the predictive capacity of bitter pit through magnesium infiltration of the fruit in commercial orchards of three locations in South Central Chile: San Fernando (SF), Curico (CU), and San Javier (SJ) was established. Three orchards were chosen in each location and for each cultivar; fruit were collected 60, 40, and 20 days before commercial harvest. Fruit were infiltrated for 2 min with magnesium chloride at 0.05 M using vacuum levels of 500 or 100 mm Hg for `Granny Smith' and `Braeburn', respectively. The predictive capacity (correlation between predicted and effective bitter pit—after 90 days at 2°C + 10 days at 18°C) increased closer to harvest; with regards to location: SF > CU > SJ. Bitter pit-like symptoms, caused by Mg infiltration stabilized 16 days after infiltration. Bitter pit incidence was better predicted than severity. Bitter pit was better predicted for `Granny Smith' than for `Braeburn'.
Richard C. Funt, M. Scott Biggs, and Mark C. Schmittgen
Physiological disorders of apples, such as cork spot and bitter pit, are a result of low soil calcium, low or excessive soil moisture, large fruit size, and environmental conditions. We report on the effect of microirrigation treatments on apple fruit when irrigation is applied as water alone or water plus a calcium (Ca)/boron (B) solution with applications applied over the tree canopy or under the tree canopy. Apples were harvested from trees in their 4th to 7th leaf and the number of fruit and size of fruit varied from year to year. In most years, there were no significant differences among treatments for fruit Ca. Fruit B was significantly higher in treatments where B was applied through the irrigation. Fruit N/Ca levels were lower when the fruit size was smaller, which was due to a higher number of fruit per tree. Year to year variations in fruit Ca levels also were likely to temperature, humidity, rainfall, fruit size, and shoot growth.