Resistance to sweet potato virus disease (SPVD) in wild East African Ipomoea

Sweet potato virus disease (SPVD), the most harmful disease of sweet potatoes in East Africa, is caused by mixed infection with sweet potato feathery mottle potyvirus (SPFMV) and sweet potato chlorotic stunt crinivirus (SPCSV). Wild Ipomoea spp. native to East Africa (J cairica, I. hildebrandtii, I. involucra and J wightii) were graft-inoculated with SPVD-affected sweet potato scions. Inoculated plants were monitored for symptom development and tested for SPFMV and SPCSV by grafting to the indicator plant J setosa, and by enzyme-linked immunosorbent assay (ELISA). Virus-free scions of sweet potato cv. Jersey were grafted onto these wild Ipomoea spp. in the field, and scions collected 3 wk later were rooted in the greenhouse and tested for viruses using serological tests and bioassays. In all virus tests, J cairica and J involucra were not infected with either SPFMV or SPCSV. J wightii was infected with SPFMV, but not SPCSV, in the field and following experimental inoculation; J hildebrandtii was infected with SPCSV, but not SPFMV, following experimental inoculation. These data provide the first evidence of East African wild Ipomoea germplasm resistant to the viruses causing SPVD.     

甘薯主要病毒病及脱毒对块根产量和品质的影响

1998～2000年利用酶联免疫吸附测定(ELISA)方法对黄淮薯区1580份甘薯样品的测定结果表明：SPFMV和SPLV是普遍存在的两种主要甘薯病毒,感染幅度分别达到20．8％～100％和2．1%～90%,SPMMV,SPCEM,C-6,SPTSV病毒在上述部分地区存在．SPCSV病毒首次在国内检测出,感染率达到8．9%。同期的标准对比试验表明脱毒种薯可显著提高鲜薯产量和商品率,7个品种鲜薯平均增产38．4％,增产幅度11．3%～92．0%．商品率(薯块大中薯率)提高23．05％．但脱毒对薯块干物质含量无显著影响。山东30处调查结果分析表明脱毒种薯随代数的增加增产幅度逐步降低,脱毒后春、夏薯产量在前3年分别平均年降低5．8％和11．7%。     

Apparent absence of viruses in most symptomless field-grown sweet potato in Uganda

Heat tolerance of groundnut (Arachis hypogaea L.) genotypes was evaluated by solute leakage and chlorophyll fluorescence techniques in heat-hardened and non-hardened plants. To determine the appropriate hardening treatment, 1-month-old plants of two groundnut genotypes, ICGV 86707 and Chico were conditioned at five combinations of hardening (37°C) and non-hardening (30°C) air temperatures over a 5-day period. Heat injury, was assessed through measurements of electrolyte leakage after stressing leaf discs to 55°C for 15 min. The relative injury was significantly influenced by the conditioning temperatures and by the temperature during 24 h prior to measurement if those involved non-hardening conditions. Relative injury and chlorophyll fluorescence were measured after stressing leaves of six genotypes at a range of temperatures between 49°C and 55°C. Significant genotype × hardening treatment interactions were observed in relative injury and chlorophyll fluorescence. Chico was susceptible to heat stress, the relative injury test identified ICGV 86707 as tolerant, and the chlorophyll fluorescence test identified ICGV 86707 as tolerant under hardened conditions and ICGV 87358 as tolerant when non-hardened. When expressed as percentage of control values, the relative injury and chlorophyll fluorescence measurements over the 49–53°C stress temperature range were strongly correlated. Chlorophyll concentrations were increased by hardening in all genotypes except Chico. In Chico, chl_b concentration was decreased and the chl_a/b ratio increased by hardening, and chlorophyll concentrations were correlated with chlorophyll fluorescence parameters. Chlorophyll concentration may therefore provide an alternative means of screening for heat tolerance.