A simple and efficient method to assess susceptibility of potato to stem rot byErwinia carotovora subspecies

Limited development of blackleg resistant potato cultivars has been ascribed to the lack of an effective and reliable test for large scale blackleg resistance screening. A method using leaf petioles was developed for assessing susceptibility of potato stems to blackleg pathogens (Erwinia carotovora subspeciesatroseptica andE. c. subspeciescarotovora). Fifty grams of sterile autoclaved silica sand in Magenta jars (GA-7 vessel, Magenta Corp., Chicago, Illinois) was drenched with bacterial suspension, (17 ml, 2.6 × 10 to 2.6 × 10⁷ cfu/ml) and freshly cut petioles from 5 to 6 week-old plants were inserted to about 5 mm into the sand. The Magenta jars with lids closed were kept on a laboratory bench (20 ±2 C, 16 hours light). The arrangement provided near ideal post-inoculation incubation environment of high humidity for pathogen multiplication and rot development in the petioles. Length of rot was recorded 72 hours after inoculation. Linear regression of rot development on inoculum concentration had R² ≥ 0.80. The petioles inoculated and incubated by this method produced measurable rot lesions with a bacterial concentration as low as 2.6 × 10⁴ cfu/ml and differentiated between the resistant cultivar Russet Burbank and the susceptible cultivar Sangre at all the inoculum concentrations used. Furthermore, susceptibility ranking of five cultivars obtained by this method agreed in general with their reported field reactions. The method is simple and sensitive, and could be used for large scale screening for stem rot resistance in wildSolanum species and early generation breeding populations.     

Soft rot and blackleg reactions in diploid potato hybrids inoculated withErwinia spp.

From 1993 to 1996 three groups of potato genotypes were evaluated for resistance toErwinia spp.: (1) 31 interspecific diploid hybrids (28 resistant and three susceptible), (2) five hexaploid or pentaploid somatic hybrids ofSolanum tuberosum (tbr) ×S. brevidens (brd), and (3) eight cultivars. Two evaluation methods were applied: tuber point inoculation with eitherErwinia carotovora ssp.atroseptica (Eca) orE. chrysanthemi (Ech) to test tuber soft rot resistance and stem base inoculation with Eca to test blackleg resistance. Some resistant diploid hybrids and somatic hybrids oftbr × brd were superior to cultivars for both tuber and stem resistance. Tuber and stem resistance toErwinia spp. in the most resistant diploid hybrids were equal to the highly resistant somatic hybrids oftbr xbrd. Tuber resistance to Eca was highly correlated to tuber resistance to Ech (r=0.815***). In two years of evaluation for stem resistance, three diploid hybrids and a derivative of one of the somatic hybrids (USA M 264) failed to develop symptoms of blackleg following inoculation with Eca, Analyses of variance for tuber and stem resistance indicated significant effects of genotype, year and genotype × year interaction. A positive relationship between tuber and stem resistance toErwinia spp. has been found, however the genetic control of resistance in tuber and stem is partially independent. In the case of Eca the correlation coefficient was r = 0.725***. Therefore it should be possible to obtain resistant genotypes to both blackleg and tuber soft rot. Several resistant diploid hybrids were selected from among those tested, which also have several other characters desirable for potato breeders.     

Efficacy of Bacillus subtilis MBI 600 Against Sheath Blight Caused by Rhizoctonia solani and on Growth and Yield of Rice

Rice sheath blight disease(ShB),caused by Rhizoctonia solani,gives rise to significant grain yield losses.The present study evaluated the efficacy of Integral?,the commercial liquid formulation of Bacillus subtilis strain MBI 600,against rice ShB and for plant growth promotion.In greenhouse studies,four log concentrations of Integral(from 2.2×106 to 2.2×109 cfu/mL) were used as seed treatment(ST).After 25 d,seedlings were dipped(SD) into Integral prior to transplanting.At 30 d after transplanting(DAT),leaf sheaths were inoculated with immature sclerotia of the pathogen.At 45 DAT,a foliar spray(FS) with Integral was applied to some treatments.The fungicide control was 50% carbendazim at 1.0 g/L,and a nontreated control was also included.Overall,there were 10 treatments,each with five replications.ShB severity was rated at 52 DAT,and seedling height and number of tillers per plant were rated at 60 DAT.In 2009,two field trials evaluated Integral at 2.2×108 and 2.2×109 cfu/mL.Integral was applied as ST,and seedlings were produced in a nursery bed.After 32 d,seedlings were treated with Integral as SD and transplanted into 10 m2 blocks.Foliar sprays were given at 45 and 60 DAT.There were seven treatments,each with eight replications arranged as a factorial randomized complete block design.At 20 DAT,the plots were broadcast inoculated with R.solani produced on rice grains.Seedling height before transplanting,ShB severity at 90 DAT,and grain yield at harvest were recorded.Integral at 2.2×109 cfu/mL provided significant increase of seedling heights over other treatments under greenhouse conditions.The Integral treatments of ST + SD + FS at 2.2×109 cfu/mL significantly suppressed ShB over other treatments.In field studies,Integral provided significant increase of seedling height in nursery,and number of tillers per plant,compared with the control.ShB severity was significantly suppressed with higher concentrations of Integral compared to lower concentrations.Grain yield were the highest at an Integral concentration of 2.2×109 cfu/mL.Overall,Integral significantly reduced ShB severity,enhanced seedling growth,number of tillers per plant and grain yield as ST + SD + FS at the concentration of 2.2×109 cfu/mL under the conditions evaluated.     

Mycoflora and Mycotoxicological Quality of Four Freshly Harvested Paddy Rice Cultivars and Relation with Harvest to Industry Reception Timing

Grain quality and safety of four freshly harvested paddy rice (Oryza sativa L.) cultivars (Epagri 109,SCS 114 Andosan,Tio Taka 113 and Epagri 115 CL) grown under irrigation system in the north of Santa Catarina State,Brazil were studied.The quality parameters evaluated were mycoflora,mycotoxins (aflatoxins,ochratoxin A and zearalenone),water distribution (moisture content and water activity) apart from environmental conditions (relative humidity and temperature) and the relation between harvest and the industry reception timing.All cultivars presented an average waiting time of 8.6 h (ranged from 0.3 to 24.9 h),a total fungi load of 8.6×104 cfu/mL (ranged from 1.8×103 to 9.4×105 cfu/mL) with a rather high humidity condition of 19.0% moisture content (varied from 14.9% to 24.5%) and 0.92 water activity (varied from 0.78 to 0.99) under the average environmental conditions of 87.3% relative humidity (varied from 80.0% to 96.8%) and 25.4 ℃ (varied from 22.5 to 27.5 ℃),respectively.The conditions to which the samples were submitted allowed fungal growth,but no mycotoxins were detected.Regarding the rice cultivars fungal genera isolated,Aspergillus and Penicillium were the most often isolated among all the cultivars and variation on fungi distribution among them was not observed.Moreover,it was not found a correlation of the grain loading & unloading time with the humidity conditions and the total fungi load.Furthermore,all results and the importance of monitoring the rice mycotoxicological quality and safety were discussed.     

Detection ofCorynebacterium sepedonicum in potato cultivars with different propensities to express ring rot symptoms

Various potato cultivars were grown in field plots from seed pieces inoculated withCoryneacterium sepedanicum by vacuum infiltration. Foliage symptoms were recorded during the growing season and tuber symptoms at harvest. Cultivars were ranked according to the frequency with which the progeny tubers expressed external bacterial ring rot symptoms. Those that yielded 50–100% symptomatic tubers were placed in symptom expression class (SEC) 1; those that produced 25–49%, 10–24%, and ≤9% symptomatic tubers were placed, respectively, in SEC 2,3, and 4. The incidence of latent ring rot infections in stems and tubers were similar among cultivars in the different SEC classes. Bacterial population densities, quantified by immunofluorescence, were as high as 10¹⁰ cells/g in stems from cultivars of all SEC classes. Mean populations in tubers ranged from 10⁶ – 10⁷ cells/g and did not differ significantly among cultivars.     

Inoculation of potato tubers withErwinia carotovora during simulated commercial washing and fluming practices

The potential for bacterial soft rot in potato tubers was affected by laboratory simulation of some components of fluming and washing practices at commercial packinghouses. The potential was expressed as disease severity (average percentage surface decayed) after a standard 4-day incubation at 20°C in a mist chamber. Increased disease resulted when there was an increase in the following factors: a) duration of immersion of tubers in water; b) population of bacteria suspended in water; c) hydrostatic pressure on submerged tubers, and d) concentration of a surfactant (Triton X-100) in the suspensions. A sample of tubers from each tuber lot was uniformly moistened with tap water and then incubated to determine a base-level disease severity. Disease severity in Russet Burbank tubers from commercial storage increased from the base-level of 0.8% to 76% when tubers were immersed in 5 × 10⁶ colony-forming units (cfu)/ml ofErwinia carotovora pv.carotovora (Ecc) for 64 min prior to incubation. Disease severity was 64% when tubers were immersed in a similar suspension for only 0.1 min, but with a hydrostatic pressure of 230 cm of water. Severity values fourto fivefold above control levels (from immersion in water) resulted from an immersion for 5 min in 5 × 10³ cfu/ml with hydrostatic pressures of 5, 180, or 370 cm of water. A 20-fold increase in severity occurred when Red LaSoda tubers were immersed briefly (less than 5 s) in 5 × 10⁶ cfu/ml. Rinsing these tubers with tap water after inoculation, but prior to incubation, did not affect the subsequent development of decay. Thus, the high potential for bacterial soft rot in tubers that have been flumed or washed by water concentrated with soft rotErwinia cannot be reduced by washes or rinses with clean water.     

Inheritance of resistance to sclerotinia stem rot (Sclerotinia trifoliorum) in faba beans (Vicia faba L.)

Stem rot, a fungal disease caused by Sclerotinia trifoliorum Eriks., is often a serious problem in many important forage legumes including faba beans (Vicia faba L.). Understanding the inheritance of resistance to the disease is essential for effective breeding of resistant cultivars. Experiments were conducted to study the inheritance of resistance to stem rot of faba beans. The F₁, F₂, and the backcross generations of five crosses between four resistant and four susceptible populations (Alto × Polycarpe, A-90 × Polycarpe, ILB-1814 × A-247, A-90 × A-244, VT × Tanagra) were used. The eight populations were crossed properly in the field, and progenies of F₁ and F₂, as well as backcross progenies of F₁ with each of their parents, were evaluated for resistance to stem rot disease under controlled conditions after artificial inoculation of the plants with carrot root pieces colonized by the fungus. On the assumption that inheritance of stem rot resistance is governed by a single dominant gene, no significant differences were found between the observed and the expected frequencies of resistance for progenies, except for one cross. As the expression of resistance to the disease fits the expected ratios for a single dominant gene model, it is concluded that the inheritance of resistance to sclerotinia stem rot in the evaluated faba bean populations is controlled by a single dominant gene.     

Evaluation of potato clones for severity of Verticillium wilt, yield and specific gravity in Maine

In 1994 and 1995, the effect of Verticillium wilt, caused byVerticillium dahliae andV. albo-atrum, on tuber yields, number and weight of U.S. No. 1 and B size tubers, and specific gravity was studied in northern Maine, an area with a short growing season. Seven clones (four resistant and three susceptible) were evaluated in a split-plot design with three replications. Clones were the whole-plot factor, and seed pieces in sub-plots were either uninoculated or inoculated with 50 ml of 4 × 10⁴ cfu/mlVerticillium spp. at planting. Individual plants were scored for Verticillium wilt symptoms before harvest on a 1= <3% wilt to 10= >97% wilt. Differences among clones for wilting and specific gravity were significant. The inoculation treatment had no effect on any of the tuber traits measured. However, there were significant clone x inoculation interactions for most tuber traits. Reductions in yield, weight and number of U.S. No. 1 potatoes, and specific gravity were greater in the Verticillium wilt susceptible clones than in the resistant clones. These results suggest that breeding clones with resistance toVerticillium spp. will reduce yield losses, while maintaining tuber size and specific gravity under disease pressure.     

解淀粉芽孢杆菌B9601-Y2提高玉米生长和产量的效应

采用促进植物生长的解淀粉芽孢杆菌B9601-Y2拌、浸玉米种子和浇灌土壤后均能显著提高玉米生长速度和生物量。3×101～3×105 cfu/mL浓度菌液浸泡玉米种子1 h,播种后5 d苗高比对照(清水)提高119.88%～168.85%;浸种2 h,3×104 cfu/mL和3×105 cfu/mL处理则有抑制作用。采用1.6×108、6.2×107、3.9×107 cfu/mL菌液浇灌土壤,播种后7 d苗重比对照增加20.75%、27.36%和33.96%。以3.9×107～1.6×108 cfu/mL浓度菌液拌种处理,15 d苗龄的植株重量比对照增加4.03%～29.35%,在收获期株高增加6.00%～16.29%,产量增加5.76%～11.81%。高浓度处理促生长效果不如中浓度处理。     

Multiplication ofPseudomonas solanacearum in resistant potato plants and the establishment of latent infections

When 1-mo-old plants of a wilt-resistant clone ofSolanum phureja (1386.15) were stem-inoculated with three strains ofPseudomonas solanacearum (K60, S123, and S206), the bacteria multiplied rapidly at the point of inoculation and then moved in the vascular system to other parts of the stem. Resistant plants showed a remarkable ability to support relatively high populations of the bacterium in the absence of disease symptoms. Although multiplication in this resistant clone was substantially less than in susceptible Russet Burbank potato plants, large numbers of bacteria (up to 624 × 10⁴ cells of K60 per 5-cm stem segment) reached the base of the stem of plants maintained at high temperature (28°C) for 20 days after stem inoculation. From the base of the stem, the bacteria moved rapidly into the roots and tubers. Strains ofP. solanacearum differed in their ability to cause latent tuber infection in different resistant potato clones. When 11S.phureja ×S. tuberosum hybrids were stem-inoculated, maintained at 28°C for 3 wk and then grown to maturity at 20°C., most of the clones yielded tubers infected by one or more strains. The race 1 strain (K60) was the most infectious; 53.8% of all tubers harvested from all plants inoculated with this isolate carried latent infections. Because one clone (BR 53.1) never yielded infected tubers, there appear to be genetic factors which may be useful in breeding programs aimed at eliminating latent tuber infection.     

Biocontrol of bacterial wilt of potato with an avirulent strain ofpseudomonas solanacearum: interactions with root-knot nematodes

Field tests for biological control of bacterial wilt of potatoes, caused byPseudomonas solanacearum, were conducted in Florida in 1984 and 1985. Potato seedpieces of tolerant (Ontario) and susceptible (Pungo and/or Atlantic) cultivars were immersed in a suspension of the avirulent, non-bacteriocinogenic strain ofP. solanacearum, B82, prior to planting in naturally-infested soil. Relatively low populations ofP solanacearum (2 to 4 log cfu/g soil) and root-knot nematodes (0 to 33 larvae ofMeloidogyne incognita/100 cm³ soil) were present in the soil before planting. In 1984, there was approximately a 50% reduction in incidence of bacterial wilt and brown rot in B82-treated plants of cultivar Atlantic, as compared with controls. With cultivar Ontario, on the other hand, disease incidence was very low and differences between treatments were not significant. In 1985, the incidence of bacterial wilt was low in all plots. Treatment with strain B82 reduced incidence of tuber brown rot in all cultivars, but differences between treatments were not significant at P = 0.05. There was a significant correlation, however, between incidence of wilt and root-knot nematode populations in the soil. Therefore, the possibility that control of bacterial wilt in 1984 was indirect,i e, via an effect of B82 treatment on root infection byM incognita, was examined. Greenhouse tests were conducted to determine the potential effect of seedpiece treatment with strain B82 on nematode infection of cultivars Atlantic and Ontario. In two out of three trials, the B82 treatment significantly reduced incidence of root knot. These results suggest that interactions of the biocontrol agent with root-knot nematodes may determine the effectiveness of a treatment designed for bacterial wilt control in the field.     

Productivity of Lotus corniculatus L. (bird's-foot trefoil) in the UK when grown under low-input conditions as spaced plants, monoculture swards or mixed swards

The dry-matter productivity of the forage legume Lotus corniculatus (bird's-foot trefoil) was assessed under low-input conditions at three sites in the north of England. An initial study in 1989 and 1990 compared fourteen accessions of L corniculatus with Trifolium repens and T. pratense grown as spaced plants at two sites with contrasting soil conditions. One site represented good agricultural land, the other poor-quality, marginal land. Yields of all species and accessions were significantly lower on the marginal site. Seasonal yields (averaged over sites) of L corniculatus cultivars averaged 52 g plant^?1 and 170 g plant^?1 in 1989 and 1990 respectively. General trends over both seasons were that T. repens and T. pratense yields were high but some L. corniculatus cultivars (Empire, Franco, Leo) and naturalized UK ‘aliens’ were similar to at least one Trifolium in each year. Yields from L. corniculatus ecotypes from the UK and Norway were very low in comparison with the cultivars. A largerscale study of eighteen L corniculatus, two L uliginosus, three T. repens and two T. pratense accessions was undertaken on an upland, calcareous site in 1990. Legumes were assessed in 2 m × 2 m swards as either monoculture or grass/legume mixture. Establishment and productivity of L uliginosus and T. pratense accessions were poor, with seasonal yields no greater that 50gm^?2 year^?1. When grown as a monoculture, L corniculatus yields were superior to both Trifolium spp., and averaged 1080 gm^?2. In mixed swards, L. corniculatus constituted a higher proportion of the total dry matter yield (26% and 62% at first and second cuts, respectively) than the other legume species. It is concluded from these studies that L corniculatus is suited to marginal or free-draining calcareous soils under low-input conditions, and consequently has more potential for use in the UK than has previously been reported.     

Reevaluation ofSolanum species accessions showing resistance to bacterial ring rot

One hundred and fifty-six plant accessions, including susceptible checks, from the IR-1 collection were evaluated for resistance/immunity to bacterial ring rot (BRR). Each accession selected had been previously rated as highly resistant to BRR based on symptom expression but, in our tests, 57 of them yielded no plants which failed to produce symptoms. However, the remaining 99, represented by a total of 2589 inoculated plants, yielded 1000 plants which failed to produce BRR symptoms after eight weeks. Immunofluorescent antibody stain testing showed that 679 of the symptomless plants supported detectable numbers ofCorynebacterium sepedonicum cells. Comparison of root-inoculated and tuber-inoculated accessions showed that root-inoculations yielded significantly fewer symptomless and bacterial cell-free plants. No significant differences were found in BRR reactions of fiveSolanum spp. when inoculated with two different strains ofC. sepedonicum. Appreciable numbers of symptomless plants were obtained from inoculated progeny of crosses with resistant cultivars but none of those retested proved to be immune.     

A detached-leaf method to evaluate late blight resistance in potato and tomato

We developed a detached leaf method for evaluating potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) germplasm for reactions toPhytophthora infestans, the causal organism of late blight. Primary leaves from the third to the sixth node of potato plants, and the fourth to sixth node of tomato plants were excised at the stem. Their petioles were inserted into 14 mm × 100 mm floral aqua tubes containing 9 ml of sterilized distilled water. The leaves in the aqua tubes were placed with abaxial sides down on galvanized metal hardware cloth (12.5 × 12.5 mm mesh). A 12.5 mm sensi-disc containing 50μl of 2 × 10⁴ zoospores was placed in the centers of the terminal leaflet and the second leaflet pair of the potato leaf. A single disc was placed on the center of the tomato leaf. The supporting hardware cloth was placed 2.5 cm above distilled water (2.5 cm deep) in 31 cm × 17 cm × 8 cm clear plastic boxes with tight fitting lids. Leaves on intact tomato and potato plants were inoculated in a similar manner and placed in a mist chamber. Lesion growth was determined 4, 5, and 6 days following inoculation. There were no significant differences in reactions to isolates ofP. infestans on detached and intact leaves of potato cultivars Green Mountain and Kennebec and the tomato cultivar Bonnie Best.     

Effects of Bacillus subtilis strain QST 713 and storage temperatures on post-harvest disease development on greenhouse tomatoes

Tomato plants in two commercial greenhouses were treated with Rhapsody (Bacillus subtilis strain QST 713, rate of 1.45%) once every 4 weeks during 2012–2013 to determine effects on post-harvest fruit infection. Populations of Bacillus and disease incidence were monitored weekly from harvested fruit over an 18-week period. Population levels of Bacillus ranged from 75 to 110 × 10⁴ colony forming units (cfu) cm⁻² of fruit surface area one week after application to 25–30 × 10⁴ cfu cm⁻² of fruit surface area 4 weeks after application. Disease incidence on harvested fruit incubated at 21 °C for 7–10 days was variable, due to variation in inoculum levels within the greenhouse as well as variable environmental conditions. Both disease incidence and severity were significantly reduced on Rhapsody-treated fruit, especially in the 1–2 week period following application. Post-harvest storage temperature (13 °C vs. 21 °C) and incubation time (12 vs. 16 days) had a significant effect on final disease severity. Rhapsody-treated fruit incubated at 13 °C had an average of 1–2% fruit infection compared to up to 20% infection on untreated fruit at 21 °C. The most frequent pathogens affecting fruit quality were Penicillium sp. and Rhizopus stolonifer. Rhapsody applications made every 4 weeks maintained sufficiently high populations of Bacillus on the fruit surface to prevent spread of these fungi onto the fruit, resulting in significant post-harvest disease control on fresh market tomatoes. When combined with storage at 13 °C for no more than 12 days, disease was reduced to negligible levels.     

Selection and morphological characterization of induced determinate mutants in sesame

The indeterminate growth habit of sesame (Sesamum indicum L.) causes non-uniform ripening of the capsules. As a solution to this problem, breeding for a determinate growth habit in sesame has become an active area of research after the discovery of dt-45, which was the first determinate mutant. The current study aimed to select new determinate mutants in locally adapted genetic backgrounds, and to describe their morphological characteristics and frequency. Consequently, the seeds of four sesame cultivars (Muganlı-57, Özberk-82, Çamdibi and Gölmarmara) were irradiated with doses of gamma rays (150-750 Gy) in two separate sets during 1994 and 1995, respectively, and the M1 populations were grown. The M2 populations were produced from the M1 progenies in both sets of experiments and also from the bulk population in the first set. Three true botanical determinate mutants (dt-1, dt-2 and dt-3) of Muganlı-57 and three short flowering period leafy determinates (dt-4, dt-5 and dt-6) of Çamdibi were selected in the M2 generations grown in Antalya, Turkey, in 1995 and 1996, respectively. Furthermore, these mutants were confirmed to breed true in the M3 and subsequent generations. Other cultivars did not yield any mutants of interest. The dt-1 mutant was similar to dt-45 and was free from the drastic changes caused by irradiation with 150 Gy. By contrast, the dt-2 and dt-3 mutants showed deformed multicarpellate capsules that were selected at the higher gamma-ray doses (300 and 400 Gy, respectively). The true botanical mutant character was recessive and monogenic, as revealed by the segregation of the M2 and M3 families. The mutation frequency for the true botanical determinates was 1.8 × 10⁻⁴ in both sets of cultivars and doses. The mutant frequency for the short flowering period mutants that were selected in the bulk population was 2.9 × 10⁻⁵. This study proved that the selection of unique mutants with a determinate growth habit is not a matter of chance; rather, it depends upon population size, the response of the cultivars to effective mutagenesis and careful screening.     

Chloropicrin Soil Fumigation Reduces <Emphasis Type="Italic">Spongospora subterranea</Emphasis> Soil Inoculum Levels but Does Not Control Powdery Scab Disease on Roots and Tubers of Potato

The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the development of powdery scab, formation of root galls and tuber yield was investigated in seven field trials conducted in Minnesota and North Dakota. Sixteen potato cultivars, with different levels of susceptibility to disease on roots and tubers, were planted in plots treated with chloropicrin at rates ranging from zero to 201.8 kg a.i. ha^?1. The amount of S. subterranea DNA in soil was determined using qPCR. Bioassays were conducted to further assess the effect of chloropicrin fumigation on root colonization by S. subterranea in two potato cultivars with contrasting disease susceptibility. In the field, chloropicrin applied at rates between 70.1 to 201.8 kg a.i. ha^?1 significantly decreased S. subterranea initial inoculum in soil but increased the amount of disease observed on roots and tubers of susceptible cultivars. The effect of increasing disease was confirmed in controlled conditions experiments. Although the amount of S. subterranea DNA in roots of bioassay plants increased with increasing chloropicrin rates, it remained similar among potato cultivars. Chloropicrin fumigation significantly increased tuber yield which in cultivars such as Shepody and Umatilla Russet were associated with the amount root galls (r = 0.30; P < 0.03). Results of these studies contradict earlier reports on the use of chloropicrin fumigation for the control of powdery scab. Factors other than inoculum level, such as environmental conditions that affect inoculum efficiency and host susceptibility, may be significant contributors to the development of powdery scab and root gall formation.     

赤霉病对陕西省主栽小麦品种品质的影响

为了解赤霉病对小麦脱氧雪腐镰刀菌烯醇(DON)毒素水平和品质指标的影响,通过喷雾及单小花滴注接种,田间弥雾保湿,对10个陕西省主栽小麦品种进行了赤霉病抗性鉴定,并对其DON毒素水平和品质相关指标进行了测定。结果表明,病情指数与千粒重呈显著负相关。喷雾接种条件下,对赤霉病表现中抗、中感的品种分别有1个、5个,其千粒重分别下降了2.84%和1.49%~8.20%;病情指数与籽粒、颖壳中的DON毒素含量呈极显著正相关,中抗品种西农511的籽粒、颖壳、穗轴中的DON毒素含量分别为14.63、24.33和56.15 mg·kg^-1,5个中感品种的籽粒、颖壳、穗轴中的DON毒素含量平均值分别为21.67、45.35、62.81 mg·kg^-1。单小花滴注接种条件下,筛选出中抗品种3个,中感品种2个,千粒重分别下降了1.38%~12.25%和2.66%~9.51%;平均严重度与籽粒、颖壳、穗轴中的DON毒素含量呈极显著正相关;3个中抗品种籽粒、颖壳、穗轴中的DON毒素含量平均分别为15.50、32.44和14.59 mg·kg^-1,2个中感品种籽粒、颖壳、穗轴中的DON毒素含量平均分别为19.98、33.80和16.41 mg·kg^-1。除苏麦3号外,喷雾接种下麦穗组织中的DON含量高于单小花滴注接种。喷雾接种条件下,病情指数与容重呈显著负相关,与蛋白质(干基)含量呈显著正相关,千粒重与容重呈极显著正相关,与蛋白质(干基)含量、稳定时间呈显著负相关,与沉降值极呈显著负相关。单小花滴注接种条件下,平均严重度、千粒重与品质指标无显著相关性,但赤霉病导致容重、蛋白质(干基)含量、湿面筋含量、沉降值、稳定时间、延展性和拉伸面积7项指标不同程度的下降。GGE双标图分析表明,7项指标中除容重外,其余指标关系密切。西农3517、西农899和西农511的综合品质表现较优。     

Influence of temperature and length of storage on resistance of potato to tuber rot induced byErwinia chrysanthemi

Tubers of 11 clones ofSolanum tuberosum subsp.andigena (andigena) and 12 cultivars ofS. tuberosum subsp.tuberosum (tuberosum) were inoculated with water suspensions (5.5 × 10⁴ 5.5 × 10⁵, 5.5 × 10⁶ CFU/ml) ofErwinia chrysanthemi. Tubers were inoculated immediately after harvest and after 6 and 16 wk of storage at 4 and 23°C. Tuber rot incidence in andigena and tuberosum increased as inoculum concentration increased. Based on tuber rot severity, clones of andigena were classified as resistant, intermediate, or susceptible and cultivars of tuberosum were classified as intermediate or susceptible. Rot severity increased in all tubers stored at 4°C and in tubers of tuberosum stored at 23°C; rot did not increase in tubers of andigena stored at 23°C. Electrolyte leakage (EL), total sugars (TS), reducing sugars (RS), non-reducing sugars (NRS) and dry matter (DM) were determined in non-inoculated tubers. There was a significant positive correlation between the rate of EL, concentration of RS and tuber rot in andigena and tuberosum. Tuber rot and DM were negatively correlated in tubers of andigena; but they were not correlated in tuberosum. Clones of andigena with low EL, TS, RS, and high DM were resistant to tuber rot, and the incidence of tuber rot in these clones was much less influenced by temperature and length of storage. The influence of temperature and length of storage on susceptibility toE. chrysanthemi may be explained by increased cell membrane permeability; increased leakage of accumulated sugars in potatoes stored at 4°C could favor bacterial proliferation resulting in more disease.     

Evaluation of the reliability of determining soft rot resistance in potatoes by the tuber slice method

Soft rot resistance in potato (Solanum tuberosum L.) tubers can be determined by inoculating tuber slices with soft rotErwinia species. Questions have been raised in the literature concerning the reliability of the tuber slice method. The objectives of this study were to 1) examine the statistical assumptions underlying the analysis of variance for different response variables as measures of soft rot resistance using the tuber slice method of evaluation; 2) estimate the sample sizes necessary to detect specified differences with power 0.83; and, 3) choose the “best” variable for measuring resistance to soft rot based on valid statistical analysis and minimal sample size. Slices from fifteen tubers from each of three cultivars (Atlantic, Norchip, Superior) were inoculated withErwinia carotovora subsp.atroseptica, E. carotovora subsp.carotovora orE. chrysanthemi and incubated at two different temperatures (20 C and 30 C) for 48 hrs. The test was conducted on two dates. Tuber samples were sliced and weighed prior to inoculation and after the macerated tissue was removed following a 48 hr incubation period. The maximum diameter of macerated tissue, actual weight loss, four measures of proportional weight loss, and various transformations of these variables were analyzed. The “best” response variables for measuring resistance to soft rot by the tuber slice method were the diameter of the macerated tissue and the square root transformation of one of the measures of proportional weight loss. No differences were found among the cultivars nor theErwinia subsp. for either of these response variables, and the cultivar ×Erwinia subsp., cultivar × temperature and cultivar ×Erwinia subsp. × temperature interactions were not significant. However, there were significant differences between the incubation temperatures, and theErwinia subsp. × temperature interaction was significant for both response variables. Estimates of sample sizes necessary to find a 20% difference in main effect and interaction effect means were calculated.