Field evaluation of yield effects on the U.S.A. heirloom sweetpotato cultivars infected by Sweet potato leaf curl virus

The incidence of Sweet potato leaf curl virus (SPLCV), a Begomovirus, on sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae), in South Carolina, U.S.A. has increased rapidly in recent years. This is likely due to the use of infected propagating materials and the increasing population of its vector, the sweetpotato whitefly, Bemisia tabaci (Gennadius). In this study, we demonstrated in field experiments that SPLCV infection reduced the yields of most heirloom sweetpotato lines relative to the yields of non-infected plants. Real-time polymerase chain reaction (PCR) technology specific to several common sweetpotato viruses was used to determine the virus infection status in 69 selected accessions of heirloom sweetpotato lines. Meristem tip culture technology was used to regenerate virus-free plants from these materials. To ensure the virus-free status, each mericlone was evaluated using real-time PCR and graft bio-indexing on the indicator species, Ipomoea setosa Ker Gawl. Mericlones of 27 cultivars were found to be free of the viruses. The 27 cultivars were included in a field test to determine the effect of SPLCV infection on yield. Yields of virus-free plants of the cultivars ranged from 10 to 80% greater than the yields of SPLCV-infected plants. However, the yield differences between virus-free and infected plants were diminished in the second year of the field experiment due to a rapid re-infection by SPLCV. These results demonstrate the importance of using certified, virus-tested seed roots or cuttings. The rapid re-infection of the virus-tested sweetpotato plants with SPLCV observed in these studies suggests that management of the whitefly population should be a critical element in control of this important virus.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

A disease survey of Fusarium wilt and Alternaria blight on sweet potato in South Africa

A disease survey was conducted on sweet potato in the major production areas of South Africa in 2006-2008 to determine the importance of wilt disease (WD) and Alternaria blight (AB) caused by Alternaria bataticola. The disease prevalence, incidence and severity were assessed for both WD and AB in 58 sweet potato fields in seven provinces, and included both commercial and resource-poor growers. The prevalence of WD in commercial fields was significantly higher than in resource-poor fields; while disease incidence and severity were very low in both commercial and resource-poor fields. Soil pH showed a moderate negative linear correlation to WD severity. WD is at present considered a minor disease of sweet potato in South Africa, although local outbreaks can be damaging. AB had very low disease prevalence, incidence and severity levels in both commercial and resource-poor fields countrywide. However, one of the fields had moderately high disease incidence and severity levels, showing that the disease can be destructive if not controlled. AB should be considered a potentially destructive disease of sweet potato in South Africa. Fusarium oxysporum was consistently isolated from WD plants, with F. oxysporum f. sp. batatas identified, but other formae speciales were also associated with the disease.     

Combining reflective mulch and host plant resistance for sweetpotato whitefly (Hemiptera: Aleyrodidae) management in watermelon

A study was conducted to evaluate the use of reflective mulch and host plant resistance for the management of the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in watermelon [Citrullus lanatus var. lanatus (Thunberg) Matsum & Nakai]. Whitefly abundance data were collected under both greenhouse (caged and uncaged) and field conditions. Consistently, a reflective mulch (also called silver or metallic) treatment resulted in a lower incidence of adult whiteflies as compared with a standard black mulch treatment. Moreover, two whitefly resistant Citrullus colocynthis (L.) Schrad genotypes, which are wild relatives of cultivated watermelon, reduced whitefly populations as compared with standard watermelon. There was generally no interaction between the mulch and genotype variables. No effect of mulch color was observed on sticky card capture of Delphastus catalinae (Horn), a whitefly predator, or on capture of an Eretmocerus sp. whitefly parasitoid in caged trials, which suggests no adverse effect on these natural enemies when using reflective mulch. Overall whitefly populations were relatively low during four seasons of field trials (2006–2009). Results from this study suggest that a combination of using reflective mulch and host plant resistance can additively suppress whitefly infestations, which have particular importance in the fast-growing organic vegetable production industry.     

Contributions of visual cues to cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), resistance in novel host genotypes

Herbivorous insects can demonstrate great selectivity among visual cues. The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) (syn. Ceutorhynchus assimilis (Paykull)) is also influenced by visual cues. Here, we present results of a study examining the attractiveness of flowers and foliage of Sinapis alba (a suboptimal host for larval development), Brassica napus (an excellent host for larval development) and novel lines derived from S. alba x B. napus; several of these have been demonstrated to be resistant in field and laboratory tests. Attractiveness, reflectance properties and resistance demonstrated in field trials were related. Responses to host plants differed among plant genotypes and were related to the amounts of UV and yellow reflected from flowers. Moderate UV reflectance greatly increased the attractive effects of yellow. Fewer weevils responded to test plants with greater or lesser floral UV reflectance.     

Biomass, extracted liquid yields, sugar content or seed yields of biofuel feedstocks as affected by fertilizer

Harvesting products from plants for conversion into renewable resources is increasing in importance. Determination of nutrition requirements for the applicable crops is necessary, especially in regions where the biofuel feedstock crops have not been historically grown. Sunflower (Helianthus annuus L.), two hybrids and one variety; sweet and grain (milo) sorghums (both Sorghum bicolor L.), one variety each, and sweet corn (Zea mays var. rugosa Bonaf.), four cultivars, were provided the recommended and twice the recommended rate of fertilizer. Biomass, expressed liquid volumes and sugar contents of sweet sorghum and sweet corn were determined. Grain yields of milo and sunflower and oil content of sunflower were determined. Sweet corn stalk sugar levels were below what is expected from field corn (maize), and were not affected by fertilizer rate. Sweet sorghum biomass and sugar content were within expected ranges and not affected by fertilizer rate. Milo grain yields were higher with increased fertilizer. Seed yield in Sunflower, which was below expected levels, was inconsistently affected by fertilizer rate, years or varieties. Overall crops year and cultivar/variety had more effect on results than did fertilizer. There does not appear to be a reason to provide fertilizer above recommended rates in production of these crops.     

Potato viruses in China

Potato (Solanum tuberosum L.) is globally the fourth largest staple crop after rice, wheat and maize. China is the largest potato producer worldwide, accounting for 26.3% and 22.2% of the global total area and yield, respectively. Viral diseases have been a limiting factor for sustainable production of potato in China. This article provides update and comprehensive information on the most important viruses, their effect on yield and their control in China. Meristem culture is currently the most widely used technique for production of virus-free potato plants and these plants are used as nuclear stock for the production of certified seed tubers. Although a significant increase in tuber yield has been achieved using certified seed potatoes, lack of application of a national seed potato production scheme has hindered progress. Conventional breeding using virus-resistant cultivars introduced from other countries as parents has already led to the production of Chinese cultivars. Use of virus-resistant wild Solanum species and genetic transformation techniques will provide new virus-resistant varieties in the future to further enhance control of potato viruses in China.     

Comparative overwintering host range of three Adelphocoris species (Hemiptera: Miridae) in northern China

In northern China, Adelphocoris suturalis, Adelphocoris lineolatus and Adelphocoris fasciaticollis (Hemiptera: Miridae) are common pests of cotton and several other crops. These species have vastly diverse geographic distribution, seasonal dynamics and abundance, the underlying causal factors of which are poorly understood. In this study, the importance of a broad range of plant species as overwintering hosts for each Adelphocoris sp. was compared. Nymphal emergence from a total of 126 plant species was monitored at two distinct locations. The eggs of A. suturalis successfully eclosed from un-plowed cotton field soil and 115 plant species, primarily pastures, weeds and agricultural crops. The eggs of A. lineolatus successfully eclosed from 40 plant species, mainly pastures and weeds. Finally, A. fasciaticollis overwintered on 35 plant species, primarily tree species, weeds and agricultural crops. In conclusion, the most common and widely distributed mirid species, A. suturalis, overwintered on a comparatively broader range of plants compared to the other two species. These observations help to understand the differences in geographical distribution and abundance of the three Adelphocoris species, and constitute the basis for forecasting and pest management protocols for Adelphocoris spp. in China.     

Both incidence and severity of white rust disease reflect host resistance in Brassica juncea germplasm from Australia,China and India

White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa, and has caused serious yield losses in Australia, China and India on both species. The first commercial B. juncea varieties are now being deployed in Australia, but their response to Australian strains of A. candida is yet to be defined under Australian field conditions. To identify useful sources of host resistance for Australia, China and India, in B. juncea, three field trials were undertaken in Western Australia. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia and 10 from China, were tested. Varying levels of host resistance to Australian strains of A. candida (race 2) were identified among the genotypes from the three countries. Genotypes CBJ-001, CBJ-003 and CBJ-004 from China consistently showed high levels of resistance to A. candida on leaves across the three trials. Overall, the genotypes from China showed the best resistance, followed by the genotypes from Australia, with those from India being the most susceptible. The most susceptible genotypes were RL1359, RH30 and Seetha from India. It is noteworthy that both the incidence and severity of disease reflected varying levels of host resistance in the germplasm from the three countries, irrespective of whether screening was undertaken in the field using natural or artificial inoculation. Differentiation of resistance among these genotypes was similar to that we reported previously for artificially-inoculated seedlings or adult plants under glasshouse conditions, indicating that a choice of options is available to plant breeders to reliably differentiate host resistance among genotypes to white rust in B. juncea.     

The effects of nitrogen rate and the ratio of NO3:NH4 on Bemisia tabaci populations in hydroponic tomato crops

Nitrogen fertilization is one of the factors that influences Bemisia tabaci (Gennadius) population density. The aim of this study was to determine the effects of three N application rates (75, 205 and 335 mg/l) and three ratios of NO₃⁻:NH₄⁺ ions (92:8, 75:25 and 55:45) in standard nutrient solution (205 mg/l N) on the population density of B. tabaci. The experiments were conducted on spring-summer hydroponic crops of tomato. The effect of plant stratum on the whitefly population was also determined. The aggregation of B. tabaci adults as well as their oviposition rate was higher at 205 and 335 mg/l N than on plants grown at 75 mg/l N. By the end of the experiment (60 d after infestation), the number of nymphs on plants at 205 mg/l N was higher than on plants at 75 mg/l N. The number of pupae was lowest on plants supplied with 75 mg/l N. An increase in NH₄⁺ percentage in standard nutrient solution (from 25% to 45% of the total N) reduced adult population density and oviposition rate. The density of nymphs and pupae, at 60 d after infestation, was lower on the tomato plants grown at 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios compared to the 92:8 ratio. The 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios resulted in a higher incidence of blossom-end rot of tomato fruit, with a lower incidence of disorder at 75:25 than at the 55:45 ratio. Plant stratum influenced adult whitefly distribution in two years of the study. Middle stratum leaves were more attractive to adults in both years. The results demonstrate the effects of N fertilization (N rate and the ratio of NO₃⁻:NH₄⁺) and plant stratum on B. tabaci population density.     

Comparative susceptibility of Ostrinia furnacalis, Ostrinia nubilalis and Diatraea saccharalis (Lepidoptera: Crambidae) to Bacillus thuringiensis Cry1 toxins

Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) are highly effective against the European corn borer, Ostrinia nubilalis (Hübner), and the closely related Asian corn borer, Ostrinia furnacalis (Guenée). Since the registration of Bt corn hybrids in the U.S. in 1996, there has been a great deal of information generated on O. nubilalis. However, relatively little information exists for O. furnacalis. To help determine whether the information generated for O. nubilalis can be leveraged for decisions regarding the use of transgenic Bt corn against O. furnacalis, experiments were designed to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species. Test insects included laboratory-reared O. furnacalis originating from Malaysia, a Bt-susceptible laboratory colony of O. nubilalis maintained at the University of Nebraska-Lincoln (UNL) and an out-group consisting of the sugarcane borer, Diatraea saccharalis (F.), from Louisiana which represents a different genus from the same family. O. furnacalis and O. nubilalis exhibited a similar pattern of susceptibility to all the Cry1 toxins and were highly susceptible to the range of Bt toxins tested including Cry1Aa, Cry1Ab, Cry1Ac and Cry1F. Both of the Ostrinia species were more tolerant to Cry1Ba compared with D. saccharalis, although sensitivity of O. furnacalis was intermediate and did not differ significantly from that of O. nubilalis and D. saccharalis. D. saccharalis was also susceptible to the range of toxins tested but unlike the two Ostrinia species, was more tolerant to Cry1F and more susceptible to Cry1Ba. These results indicate that both of the Ostrinia corn borer species are similar in sensitivity to the Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F toxins, thus suggesting shared toxin receptors and mechanisms of toxicity for the two species.     

Characterization of Solanum chomatophilum resistance to 2 aphid potato pests, Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer)

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) are responsible for yield reduction in potato (Solanum tuberosum) production by direct phloem feeding and by spreading viruses. Breeding resistant traits from Solanum chomatophilum into the potato germplasm provides alternative means to control aphid infestations. Integrated pest management strategy, using plant resistance, benefits from the characterization of the resistance and of its impact on aphid biology. Our objective was to characterize the resistance of S. chomatophilum by assessing the effects of accessions, plant parts on aphid performance, and by assessing the impact of the resistance factors on different aphid developmental stages and on alate morph production. Detailed aphid performance was obtained by measuring fecundity, survival, percentage of nymphs that reached adult moult, and population growth using whole plant and clip cage experimental designs. Accession and plant physiological age, but not aphid developmental stage, influenced all life-history parameters, except for alate morph production which was not induced on the resistant accessions. Plant part influence was independent of plant species and accession. Both experimental designs resulted in congruent resistance levels at the accession level for each of the two aphid species, supporting the use of any of them in S. chomatophilum resistance screening. PI243340 was resistant to both aphid species, while PI365324 and PI310990 were also resistant to M. euphorbiae and M. persicae, respectively.     

侵染湖南甘薯种质资源的曲叶病毒和杆状病毒的检测及其亲缘关系分析

采用PCR技术对2015—2016年从湖南省多个市县采集的180份甘薯种质资源进行两种DNA病毒（sweet potato leaf curl virus,SPLCV和sweet potato badnavirus,SPBV）检测,并以PCR扩增产物序列为基础,对这两种病毒的亲缘关系进行分析。结果表明：（1）180份甘薯种质资源中,22份检测出SPLCV,占总数的12.2%;32份检测出SPBV,占总数的17.8%;8份同时检出SPLCV和SPBV这两种病毒,占总数的3.9%。（2）检出SPLCV的市县有长沙、永州、怀化、邵阳、郴州、常德、娄底、益阳、岳阳和株洲;检出SPBV的市县有长沙、永州、怀化、衡阳和邵阳;检出两病毒复合侵染的市县有怀化、长沙、永州和邵阳。（3）基于病毒全基因组序列分析显示,全球已报道的36个SPLCV分离物可分为3组,本研究获得的12个湖南分离物可分别归于3个组中,其中6个归于组Ⅰ,1个归于组Ⅱ,5个归于组Ⅲ,表明湖南SPLCV具有高度多样性。（4）基于病毒运动蛋白和外壳蛋白编码基因部分序列分析显示,全球已报道的36个SPBV分离物可分为4组,绝大部分分离物属于组Ⅰ,我国1个安徽分离物单独成组（组Ⅱ）,我国2个山东分离物和1个海南分离物构成1个组（组Ⅲ）,本研究获得的2个湖南分离物其中1个归于组Ⅰ,而另1个与已报道各分离物的核苷酸序列均存在显著差异,相似性仅为74.92%,单独成组（组Ⅳ）,表明我国SPBV具有高度的变异性,存在多个变异类型。本研究结果可为湖南地区这两种病毒病防控提供依据。     

Effects of different brassicaceous host plants on the fitness of Pieris brassicae (L.)

Pieris brassicae (L.) is a destructive cosmopolitan pest of cruciferous crops. It is present wherever its host plants occur and it is considered to be one of the most widely distributed of all the Lepidoptera. We investigated the affect of various host plants on the fitness of P. brassicae to survive, develop and reproduce. We quantified development time, survival and mortality on cabbage (Brassica oleracea capitata), cauliflower (Brassica oleracea botrytis), radish (Raphanus sativus), broccoli (Brassica oleracea italica), and mustard (Brassica campestris) under laboratory conditions. The developmental time from eggs to adult eclosion was the shortest (30.3 days) on cabbage and the longest (38.0 days) on radish. However, adult longevity was significantly (P < 0.001) greatest on cabbage compared with the other host plants tested. Similarly, the developmental rate of P. brassicae was found to be faster on cabbage than other cole crops. Moreover, the lowest immature mortality was evident on cabbage and highest on mustard and radish. Differences in reproductive parameters of the P. brassicae among host plants were analyzed using pseudo-values, which were produced by jackknife re-sampling. The data showed that the higher intrinsic rate of natural increase (0.116 females/female/day) was found on cabbage. Cabbage was recognized as the most suitable host for P. brassicae because of shorter developmental period, higher percentage survival, lower doubling time (6.00), and higher number of adult emergence (29.7%).     

Effects of host plant on the development, survivorship and reproduction of Dysmicoccus neobrevipes Beardsley (Hemiptera: Pseudoccocidae)

The effects of four host plants (Agave sisalana, Ag. americana var. marginata, Ananas comosus Baili and An. comosus Smooth Cayenne) on the biology of the mealybug Dysmicoccus neobrevipes Beardsley were studied in the laboratory at 26 ± 1 °C, 75-90% RH and 14:10 (L:D) photoperiod. The development, survivorship, longevity, reproduction and life table parameters of D. neobrevipes differed among the host plants. The shortest developmental period (from the first instar nymph to adult) was recorded on An. comosus Smooth Cayenne (22.4 days for females and 21.3 days for males), whereas the longest was recorded on An. comosus Baili (25.6 days for females and 24.7 days for males). The highest survivorship was found on An. comosus Baili (98% for both females and males) and the lowest was on Ag. americana var. marginata (39.6% for females and 50% for males). Meanwhile the sex ratio and fecundity were highest and the pre-lay period was shortest on Ag. sisalana. The longest longevity of females was 62.5 days on An. comosus Baili, whereas the other host plants did not differ significantly with grand mean longevities of 51.0 days for females, while the longest and shortest longevities of males were 4.6 days and 2.3 days on Ag. americana var. marginata and Ag. sisalana, respectively. Values for net reproductive rate, intrinsic rate of increase and finite rate of increase were highest on Ag. sisalana, whereas the mean generation time was shortest on An. comosus Smooth Cayenne. The results indicated that Ag. sisalana is the most suitable host for D. neobrevipes among the four tested plants. When reared on Ag. sisalana, D. neobrevipes had a short developmental period (females 22.7 days and males 23.8 days), high reproduction (418 nymphs/female) and a high intrinsic rate of increase (0.106). Results of this study indicated that host plant can largely influence the population dynamics of D. neobrevipes, and our findings are useful in understanding the roles of host plants in integrated management of this pest, including exploitation of these host plants in push-pull control.     

Manihot flabellifolia Pohl,wild source of resistance to the whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae)

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P < 0.05). Development time was not significantly different, ranging from 35–40 days on accessions and MEcu72 and 33.5 days on CMC-40 (P < 0.05). In contrast, the population growth rate (r_m) was significantly lower on the M. flabellifolia accessions, with Fla 61 standing out with a growth rate 98 and 99% less than that obtained on MEcu72 and CMC-40, respectively. Once the resistant levels have been identified to A. socialis on the M. flabellifolia accessions, interspecific crosses of M. esculenta subsp. M. flabellifolia and backcross programs could be developed to incorporate the desirable characteristics from the wild relatives into elite progenitors of M. esculenta.     

Insecticidal activities of crude extracts and phospholipids from Chenopodium ficifolium against melon and cotton aphid, Aphis gossypii

Several organic solvent extracts of Chenopodium ficifolium were tested for their insecticidal activity against melon and cotton aphid, Aphis gossypii, on cucumber plants. Both methanol and ethanol extracts, at 5000 μg ml⁻¹, were highly active giving over 80% control. The other crude extracts displayed moderate or weak insecticidal activity giving control in the range of 16–69%. Two phospholipids were isolated as insecticidal active substances from C. ficifolium. Their chemical structures were identified as 1-palmitoyl-2-(3-trans)-hexadecenoyl-sn-glycero-3-phosphoglycerol and 1-palmitoyl-2-linoleoyl-3-glycerophosphocholine by GC–MS, EDS, mass and NMR spectral analyses. Both compounds displayed a dose-dependent mortality of A. gossypii. Furthermore, the liquid formulation that was obtained by partitioning with n-hexane from the methanol extract of C. ficifolium controlled melon and cotton aphid on cucumber plants effectively. These results indicate that extracts of C. ficifolium have potential for development as botanical insecticides for controlling A. gossypii infesting cucumber plants.     

Pre-harvest survival of codling moth in artificially infested sweet cherry fruits

Prior to the 2009 season, sweet cherry fruits, Prunus avium (L.) L., from North America were required to be fumigated with methyl bromide before being exported to Japan to eliminate possible infestation by codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae). However, based on recent biological research on host status, a new procedure (the “systems approach”) was implemented relying on the cumulative effects of pre- and post-harvest practices to produce pest-free sweet cherry fruits for export. This is an organized process that involves the integration of procedures used in the production, harvest, packaging, and distribution of a commodity which cumulatively meet the requirements for quarantine security. The objective of our study was to provide additional information to support the systems approach for codling moth in sweet cherries fruits. For four seasons, branches with sweet cherry fruits were caged on trees and infested by released ovipositing codling moths into the cages. Fruits were sampled weekly for codling moth individuals at each life stage. Eggs were laid mostly on leaves with the seasonal average numbers per cage ranging from 142 to 617. Populations declined rapidly after egg eclosion, with <1.5% of the original cohort surviving to fifth instars. Even after 8 weeks, none had formed cocoons or pupated. This failure of the codling moth to complete a life cycle under field conditions supports previous life history studies and demonstrates that sweet cherry fruits are inadequate hosts for codling moth.     

Effects of after-ripening and storage regimens on seed-germination behavior of seven species of Physaria

The after-ripening response has been well documented in many plant species but studies of this topic are lacking in many new oilseed crops such as Physaria. In a factorial experiment, we tested the effect of different after-ripening periods and germination conditions on freshly harvested seeds of seven Physaria species, Physaria argyraea, Physaria fendleri, Physaria gracilis, Physaria rectipes, Physaria recurvata, Physaria sessilis, and Physaria thamnophila. The seeds were stored for 4 and 12 weeks over two saturated salt solutions (LiCl and MgCl₂) to equilibrate seed moisture at three storage temperatures (5, 25, and 35 °C). We likewise tested a dormancy-breaking protocol on these species by using conditions previously recommended for use in genebanks for P. fendleri. The germination tests were conducted with light (1052 lux) and gibberellic acid (GA₃) (100 ppm) and without them. Results suggested that conditions previously set for P. fendleri are also adequate for P. gracilis, P. recurvata, and P. sessilis, but may still be not optimal for the perennial species, P. argyraea, P. thamnophila, and P. rectipes. Overall, higher germination percentages were obtained with light and GA₃ treatments. In all species, we observed slight differences between total germination results after 4 weeks and 12 weeks of storage, with higher values evident only in P. fendleri, P. recurvata, and P. thamnophila after their fresh seeds were subjected to 12 weeks of after-ripening at warm temperatures.     

Population dynamics of Xanthomonas campestris pv. vitians on different plant species and management of bacterial leaf spot of lettuce under greenhouse conditions

The population dynamics of Xanthomonas campestris pv. vitians (Xcv) was studied both externally and internally in lettuce, tomato and pepper plants. In addition, the application of bactericides during transplant production period was carried out for the management of bacterial leaf spot of lettuce under greenhouse conditions. Epiphytic populations of Xcv were recovered on leaves of lettuce plants (10⁵ CFU/g) 5 weeks after sprayed than the other plant species when inoculated with 10⁸ CFU/ml of Xcv. When plants of each crop species infiltrated with the bacterium at 10⁵ CFU/ml, the highest populations were developed in lettuce (10⁸ CFU/cm²) followed by pepper with 10⁶ CFU/cm² and tomato with 10⁵ CFU/cm² 10-days after infiltration. Application of a mixture of Maneb and Kocide or Kocide alone as a foliar spray on lettuce significantly reduced the incidence and disease severity of bacterial leaf spot by 29 and 27% respectively. Spread of the bacterium and development of the disease may partly be managed by avoiding intercropping of these plants commonly grown in close proximity to lettuce. For the management of leaf-associated populations of Xcv in lettuce, use of a mixture of Maneb and Kocide is advocated to minimize the effect of attacks.