Damage of potato tubers,a review

Summary Damage to potato tubers due to mechanical forces is among the most important causes of loss of quality reported throughout the world. The causes of such damage are mechanical injuries that occur primarily in association with harvesting and grading. The extent of damage is dependent on the condition of the tubers and also reflects the history of the potatoes. Although important advances have been made, there is still a considerable need for research on this subject since knowledge of the combined effects of essential physiological proceses within the cells is still lacking. The avoidance of exposure to mechanical forces constitutes the most effective protection against tuber damage.     

Soil and tuber calcium affecting tuber quality of processing potato (Solanum tuberosum L.) cultivars grown in Hokkaido,Japan

Calcium (Ca) nutrition for potato (Solanum tuberosum L.) is important to increase tuber Ca concentration and improve potato tuber yield and quality. High tuber Ca content among other benefits mitigates incidence of blackspot bruise through maintenance of membrane health and regulation of biochemical reactions that leads to potato tuber discoloration. However, growers avoid application of Ca fertilizer in potato production in the belief that it causes potato common scab in Hokkaido, Japan. This study was conducted in Hokkaido to determine the current status of soil Ca and tuber Ca content levels, and its effect in mitigating incidence of potato bruise. Soil and tuber samples were collected from 90 and 80 fields in Tokachi and Kamikawa districts, respectively, in 2013 and 2014. Soil samples were analyzed for base saturation, Ca saturation, and exchangeable Al. Tuber Ca content and susceptibility of tubers to bruising were also evaluated. This study found that (1) 81% and 76% of soils collected from Tokachi and Kamikawa district, respectively, were deficient in Ca level, (2) tuber Ca content was lower than the reported value (250 mg kg^?1) considered to mitigate incidence of bruise, and (3) incidence of bruise were influenced by both tuber specific gravity and Ca content. There is urgent need to apply Ca fertilizer to attain increased soil Ca levels and improve quality of tubers.     

Recurrent breeding method enhances the level of blackspot (Didymella pinodes (Berk. & Blox.) Vestergr.) resistance in field pea (Pisum sativum L.) in southern Australia

Blackspot, caused by Didymella pinodes (Berk. & Blox.)Vestergr., is one of the most important diseases of field pea, causing significant reduction in seed yield and quality in southern Australia and in other parts of the world. Development of resistant germplasm has been slow because of the low level of resistance found in the available germplasm, poor reliability of screening methods and the polygenic nature of inheritance. Crosses were made between agronomically suitable lines and resistant germplasm from different sources. Their progeny were advanced through the single seed descent method and single plants were selected at F₄/F₅. The F₄/F₅ derived lines were screened against blackspot in the field under disease pressure and evaluated for grain yield at multilocations over 2 years. Despite the low level of resistance in the parental germplasm, the level of resistance has increased significantly in the new germplasm. Many of the resistant lines were late and low yielding, but lines with higher resistance and early flowering and high yield potential were also identified indicating that the disease resistance, adaptation and yield potential can be combined. However, the resistance identified in this study is only partial and suitable agronomic practices may need to be supplemented to minimise the yield loss and enhance the benefits of this partial resistance.     

Importance of chlorogenic acid on the oxidative potential of potato tubers of two German cultivars

Summary Two German cultivars differing in blackspot susceptibility were grown in pots in 1998 and 1999 under control and water stress conditions. Blackspot susceptibility of the tubers was defined as oxidative potential. The effect of free tyrosine, cysteine, phenylalanine, chlorogenic and ascorbic acid on the oxidative potential was analyzed. A high concentration of ascorbic acid led to a decrease in the oxidative potential after harvesting in 1998. No correlation was found between oxidative potential and free tyrosine, phenylalanine or cysteine, respectively. Chlorogenic acid content increased during storage and gave a significant correlation with discoloration, showing that it can have an effect on the oxidative potential of the tuber greater than previously thought. Supplementing freeze-dried potato samples with pure chlorogenic acid increased the oxidative potential. Oxidative potential seems to depend on a series of chemical compounds, and their content is affected by factors including annual variations, cultivar, water availability and storage.     

Subcutaneous tissue discoloration in ware potatoes. 1. A chain analysis in the Netherlands

Summary In the chain of handling operations from harvesting to packaging inclusive, potatoes are exposed to many brief mechanical forces (impacts) and to long-term pressure. Impact and pressure can lead to subcutaneous tissue discoloration causing qualitative and quantitative losses. We investigated the characteristics of construction and utilization of representative Dutch ware potato handling chains and found that the number and height of drops appeared to be too high, the use of cushioning materials insufficient and the speed of the transporting parts too high and not in balance with each other. The contribution to the total amount of subcutaneous tissue discoloration was 16% for the harvesting to bin filling phases inclusive, 22% for the storage phase, 27% for the shovelling to truck loading phases inclusive and 35% for the truck unloading to packaging phases inclusive. These contributions varied considerably within phases and within links. The results can be used to develop equipment, upgrade present chains and design new, produce-frendly handling chains.     

月季黑斑病的流行与防治

本试验采用对样枝分级,且不断更替的取样方法,进行了14个月的月季黑斑病流行的系统调查。月季黑斑病在广州地区周年发生,有2个主要的流行时期,分别在4月下旬至7月上旬及9月下旬至10月下旬。其流行与温度、湿度、降雨量及降雨次数密切相关,在适宜的温度(20—27℃)下,降雨或相对湿度高峰10—20天内出现病叶率高峰。田间10种药剂防病试验,敌力脱效果最高,达91.2％;施保克次之,为86.7％。百菌清也具有良好的防效,3年均在70％以上;如果与营养液1号混合喷雾,不仅防效提高,还可以促进月季生长、增加花枝数量和提高切花质量。     

Dietary protein/lipid level and protein source effects on growth,tissue composition and lipid metabolism of blackspot seabream (Pagellus bogaraveo)

A study was carried out to determine the effects of fish meal (FM) replacement by plant protein (PP) on growth, body composition and lipid metabolism of blackspot seabream fed different protein/lipid levels. Four experimental diets were formulated to contain two protein (P) and lipid (L) levels (60P/6L or 50P/10L), varying in their protein source (100% FM or 50% FM: 50% PP). Dietary inclusion of PP did not affect growth of fish fed 60P/6L, although fish fed 50P/10L exhibited lower final body weight and daily growth index. Fish fed 60P/6L presented the highest protein and the lowest lipid content. FM replacement by PP has decreased muscle n‐3 whereas the n‐6 fatty acids increased. Glucose‐6‐phosphate dehydrogenase and fatty acid synthetase (FAS) were depressed in fish fed 50P/10L. FAS was significantly increased with 60P/6L PP which was positively correlated with lipid retention data. Those results suggest the conversion of other nutrient than lipid (protein and/or carbohydrates) into corporal fat. Hepatic lipoprotein lipase activity was lowest in fish fed PP diets. Plasma glucose peaked 1–2 h postfeeding, in all groups and was generally higher with 60P/6L FM. This work shown that besides dietary P/L level, protein source has a strong effect on species lipogenesis and lipid retention. Hence, the 50P/10L FM diet was the most cost‐effective for blackspot seabream juveniles.     

Relationship between ascochyta blight on field pea (Pisum sativum) and spore release patterns of Didymella pinodes and other causal agents of ascochyta blight

Ascochyta blight of field pea, caused by Didymella pinodes, Phoma medicaginis var. pinodella, Phoma koolunga and Didymella pisi, is controlled through manipulating sowing dates to avoid ascospores of D. pinodes, and by field selection and foliar fungicides. This study investigated the relationship between number of ascospores of D. pinodes at sowing and disease intensity at crop maturity. Field pea stubble infested with ascochyta blight from one site was exposed to ambient conditions at two sites, repeated in 2 years. Three batches of stubble with varying degrees of infection were exposed at one site, repeated in 3 years. Every 2 weeks, stubble samples were retrieved, wetted and placed in a wind tunnel and up to 2500 ascospores g^?1 h^?1 were released. Secondary inoculum, monitored using seedling field peas as trap plants in canopies arising from three sowing dates and external to field pea canopies, was greatest in early sown crops. A model was developed to calculate the effective number of ascospores using predictions from G1 blackspot manager (Salam et al., 2011b; Australasian Plant Pathology, 40 , 621–31), distance from infested stubble (Salam et al., 2011a; Australasian Plant Pathology, 40 , 640–7) and winter rainfall. Maximum disease intensity was predicted based on the calculated number of effective ascospores, soilborne inoculum and spring rainfall over two seasons. Predictions were validated in the third season with data from field trials and commercial crops. A threshold amount of ascospores of D. pinodes, 294 g^?1 stubble h^?1, was identified, above which disease did not increase. Below this threshold there was a linear relationship between ascospore number and maximum disease intensity.     

Rice protein concentrate meal as potential dietary ingredient in practical diets for blackspot seabream (Pagellus bogaraveo)

The aim of this study was to evaluate the performances and the flesh quality of Pagellus bogaraveo fed with diets containing rice protein concentrate [RPC, 70% crude protein (CP) and 10% ether extract]. Three isoproteic and isoenergetic (CP 47%, 22 MJ/kg DM) diets were formulated with an increasing level of RPC: 0%, 20% and 35%. The fish (mean weight 75 g) from the Messina Straits were randomly distributed in 12 tanks (3 diets x 4 replications, 10 fish/tank). The daily ratio (1.5% of the fish biomass) was updated every 15 days. Biomass gain showed an opposite trend to the RPC diet inclusion. No differences appeared in the somatic indexes. Differences appeared between fatty acid profiles of the dorsal muscle. Fatty acid of series n-6 increased and fatty acid of series n-3 decreased in fillets of fish fed with increasing levels of RPC. The inclusion of RPC in the diets, as a partial replacement of fish meal (20%), is possible without affecting the growth performance and fillet quality.     

Isolation of lymphocystis disease virus from sole, Solea senegalensis Kaup, and blackspot sea bream, Pagellus bogaraveo (Brunnich)

Two viruses were isolated from cultured sole, Solea senegalensis, and wild blackspot sea bream, Pagellus bogaraveo, and preliminarily characterized as lymphocystis disease viruses (LCDVs). Viral isolates were characterized by morphological, biochemical and biophysical properties. In addition, the susceptibility of four fish cell lines was also tested. LCDV isolates developed cytopathic effects on the SAF-1 cell line at 5 and 6 days post-infection and reached titres of 10(6) TCID50 mL(-1). The antigenic and structural protein analysis of the two new LCDV isolates showed identical profiles to that obtained for LCDV strain Leetown NFH (ATCC VR-342), used as a reference viral strain, and for an LCDV isolate collected from gilt-head sea bream, Sparus aurata, cultured in southern Spain. Molecular confirmation was performed by polymerase chain reaction. Specific primers for LCDV produced a 270-bp DNA fragment, the expected size for LCDV.