. There is currently no report of hot water treatment or heated fungicide treatment to delay CBS lesion development on citrus fruit after harvest. The objective of this study was to investigate whether hot water or heated fungicide treatments can reduce
Jiaqi Yan, Megan M. Dewdney, Pamela D. Roberts and Mark A. Ritenour
Galen Peiser, Gloria López-Gálvez, Marita Cantwell and Mikal E. Saltveit
Russet spotting is a physiological disorder of lettuce (Lactuca sativa L.) caused by exposure to hormonal levels (<1 μL·L-1) of ethylene in air at ≈5 °C. Enhanced phenolic metabolism and the accumulation of phenolic compounds accompany the appearance of brown, oval lesions on the leaf midrib. Phenylalanine ammonia-lyase (PAL) is the first committed enzyme in the phenylpropanoid pathway. Three inhibitors of PAL activity [2-aminoindan-2-phosphonic acid (AIP), α-aminooxyacetic acid (AOA), and α-aminooxi-β-phenylpropionic acid (AOPP)] greatly reduced the accumulation of phenolic compounds and browning of lesions. At a concentration of 50 μm, AIP inhibited the formation of chlorogenic and dicaffeoyl tartaric acids in cut midribs of iceberg lettuce by 92% and 98%, respectively. AIP competitively inhibited PAL activity from a lettuce midrib homogenate with an apparent Ki of 22 nm. While the formation of phenolic compounds was strongly inhibited by AIP, the number of lesions associated with russet spotting was not affected. Only the color of the lesions was affected by AIP. In control midribs the russet spotting lesions were brown while those in the AIP-treated midribs were initially olive green and after 3 to 7 days these lesions turned the characteristic brown color. No tyrosine ammonia-lyase activity was detected in a homogenate of lettuce midrib tissue. These results indicate that the early development of russet spotting lesions is independent of the increase in PAL activity and phenolic compounds rather than an effect of these increases as previously suggested. However, accumulation of phenolic compounds does contribute to the subsequent browning symptoms indicative of russet spotting.
Joshua K. Craver, Chad T. Miller, Kimberly A. Williams and Daniel L. Boyle
determine cellular layers involved in lesion development to evaluate differences and similarities in abnormal cellular growth among the species. Materials and Methods Plant materials. Rooted cuttings of ornamental sweetpotato were obtained from a commercial
Jeffrey A. Anderson, Alexander B. Filonow and Helen S. Vishniac
One strategy to reduce postharvest losses of fruits to pathogens is to introduce organisms with biological control capabilities. Our objective was to determine the effectiveness of two yeast isolates in inhibiting lesion development caused by Botrytis cinerea (Bc) on freshly harvested apples differing in maturity. `Golden Delicious' apples were harvested on 29 Aug., 23 Sept., and 10 Oct. 1995. Apples receiving the seven treatments [control, wound, Cryptococcus humicola (Ch), Sporobolomyces roseus (Sr), Bc, Ch + Bc, Sr + Bc] were placed in plastic boxes with damp paper towels. Each day for 7 days, ethylene production and lesion diameter at the wound were recorded. Ethylene production was not affected by treatment, and increased with later harvest date. Lesion diameter on apples treated with Bc was smaller on the first harvest than on the second and third harvests. Sr provided partial control on the second and third harvests, and Ch completely inhibited lesion development except for day 7 of the third harvest.
Jeff Anderson, Alexander B. Filonow and Helen S. Vishniac
Strategies to reduce postharvest losses of fruit to pathogens include low-temperature storage, fungicides, and use of organisms with biological control capabilities. Our objective was to determine the effectiveness of two yeast isolates in inhibiting lesion development caused by Botrytis cinerea (Bc) on freshly harvested apples of different maturity. `Golden Delicious' apples were harvested on 29 Aug., 23 Sept., and 10 Oct. 1995. Apples comprising the seven treatments [control, wound, Cryptococcus humicola (Ch), Sporobolomyces roseus (Sr), Bc, Bc + Ch, Bc + Sr] were placed in plastic boxes with damp paper towels. Each day for 7 days, ethylene and CO2 production and lesion diameter at the wound were recorded. Ethylene and CO2 production were not affected by treatment. Lesion diameter on apples treated with Bc was smaller on the first harvest, compared with the second and third harvests. Sr provided partial control on the second and third harvests, and Ch completely inhibited lesion development on all harvests.
William S. Bramlage
On Granny Smith apples, scald development exhibits characteristics that are typical of chilling injury. Yet, when `Cortland' and `Delicious' apples were placed in loosely closed polyethylene bags and kept continuously at 20C, scald-like injuries began to occur after 2 weeks. Lesions were predominantly expressed as lenticel spotting and as bronzing in the calyx cavity, which are not typical of superficial scald, but some typical scald lesions did develop on the shaded sides of the fruit. Lesion development decreased with later harvest of fruit. Fruit enclosed in poly bags accumulated high concentrations of α-famesene and conjugated trienes in their peel. Whether or not scald should be considered to be a chilling injury will be examined in light of these contrasting results.
B.M. Pryor, R.M. Davis and R.L. Gilbertson
The susceptibility of 46 carrot cultivars to infection by Alternaria radicina Meier, Drechsler, and Eddy, causal agent of black rot disease, was evaluated in field trials with a toothpick inoculation method. Toothpicks infested with A. radicina were inserted into the shoulders of 10- to 12-week-old carrots (Daucus carota L.) and lesion areas were measured 9 to 10 weeks later. There were significant differences in lesion size among cultivars. Relatively resistant cultivars included `Panther' and `Caro-pak', and susceptible cultivars included `Royal Chantenay' and `Nogales'. Nine of the cultivars were inoculated with A. radicina-infested toothpicks and maintained in cold-storage for 10 weeks. Lesion development was greater in cold-storage than in the field, but the relative ranking of cultivars in terms of resistance to A. radicina was similar.
T.M. Gradziel and Dechun Wang
Rate of brown rot lesion development following inoculation with Monilinia fructicola (Wint.) honey varied within clingstone peach (Prunus persica (L.) Batsch) germplasm evaluated in 1990 and 1991. High levels of resistance were identified in selections derived from the Brazilian clingstone peach cultivar Bolinha. Resistance appeared to be limited to the epidermal tissue. No relation was detected between brown rot resistance and concentration of phenolic compounds or polyphenol oxidase activity in the susceptible California germplasm. An inverse relation was observed between disease severity and rating for phenolic-related discoloration when `Bolinha' derived selections were analyzed. A moderate positive correlation was observed for all germplasm tested between genotype means for phenolic content and enzymatic browning. Any causal relationship, if it exists, between phenolic content and brown rot resistance is obscured by an array of physical and chemical changes in the maturing fruit.
Sandra E. Branham, Mark W. Farnham, Shane M. Robinson and W. Patrick Wechter
Bacterial leaf blight incited by Pseudomonas cannabina pv. alisalensis (Pca) is a devastating disease with incidence reports worldwide and a wide host range capable of infecting all commercially valuable Brassica crops. With no chemical control options available, the most effective form of disease control is host plant resistance, but thus far resistant germplasm has only been identified in Brassica juncea L. (mustard greens). We report the first screening of Brassica oleracea L. var. viridis germplasm, including leafy green collard and collard-like accessions, for resistance to bacterial leaf blight by artificial inoculation of Pca in greenhouse trials. All commercial cultivars tested displayed an intermediate disease response resulting in leaf lesion development that renders the product unmarketable. Two sources of significant resistance were identified in the U.S. Department of Agriculture (USDA) viridis collection, which provides a valuable source of resistance alleles for collard cultivar development and introgression into other B. oleracea crops.
Charles S. Krasnow and Mary K. Hausbeck
Phytophthora capsici annually threatens production of cucurbit and solanaceous crops. Long-lived oospores produced by the pathogen incite primary infection of susceptible plants when conditions are wet. Limiting the rot of winter squash and pumpkin (Cucurbita sp.) fruits is difficult due to the long maturation period when fruits are often in direct contact with infested soil. Genetic resistance to fruit rot is not widely available within Cucurbita sp.; however, age-related resistance (ARR) to P. capsici fruit rot develops in specific cultivars during maturation. The objective of this study was to evaluate the fruits of 12 cultivars of Cucurbita pepo, Cucurbita moschata, and Cucurbita maxima for ARR to P. capsici using a mycelial-plug inoculation method. All Cucurbita pepo and Cucurbita moschata cultivars displayed ARR; 7 days postpollination (dpp) fruits were susceptible, limited lesion development occurred on fruits 22 dpp, and lesions did not develop at 56 dpp. Disease developed on both Cucurbita maxima cultivars tested at 7, 14, 22, and 56 dpp. Firmness of fruit exocarps was measured with a manual penetrometer. Exocarp firmness of all cultivars increased during maturation; however, there was no correlation between firmness and disease incidence among cultivars at 22 dpp (R 2 = −0.01, P = 0.85). When fruits of cultivars expressing ARR at 22 dpp were wounded before inoculation, fruit rot developed.