Pedigree selection for Gibberella ear rot resistance in maize

The pedigree method is often used for developing inbred lines in maize (Zea mays L.). This study was conducted to assess the effectiveness of pedigree selection for improving resistance to Gibberella ear rot in four maize populations. Selection was based on the severity of ear rot symptoms after inoculation with macroconidial suspensions of Fusarium graminearum (Schwabe) into the silk channel (for two populations) and into the developing kernels (for two other populations). Samples of the selfed families (S₁ to S₅), recovered from remnant seed from the selection programs, were evaluated for disease resistance during three years, using inoculation and evaluation protocols similar to those used during selection. Among-family selection was effective in both of the populations selected after silk inoculation and in one of the populations selected after kernel inoculation. Responses to selection were more evident in later than in earlier generations for both types of inoculation. Changes in the estimated genetic gain over generations were consistent with changes in the variances among families, which tended to increase in early generations and to decrease in later generations. Selection after kernel inoculation seemed to have been more effective than selection after silk inoculation in developing families with more stable resistance. Based on the results obtained here, it seems that responses to family selection could be accelerated without increasing operational costs by increasing selection intensity in later generations and inoculating fewer plants per family.     

Stability of maize resistance to the ear rots caused by Fusarium graminearum and F. verticillioides in Argentinian and Canadian environments

Sources of resistance to Fusarium spp. are needed to develop maize hybrids resistant to the accumulation of fungal mycotoxins in the grain. In a search for resistant germplasm in 1999 and 2000, a set of Argentinian maize populations was evaluated in Ottawa, Canada, for resistance to ear rots after inoculation with local isolates of Fusarium verticillioides and F. graminearum. Sixteen of these populations, varying in observed resistance levels, were re-evaluated in 2003 and 2004 in Pergamino, Argentina, using local isolates of the same fungi. Conidial suspensions of each fungal species were inoculated into the silk channel of primary ears. Disease severity was assessed after physiological maturity using a scale based on the percentage of visibly infected kernels. Genotype effect was more important than genotype-by-fungal species or genotype-by-fungal species-by-environment interaction effects. In addition, disease severity levels associated with each fungal species were positively correlated (P < 0.05) (r = 0.90, r = 0.81, r = 0.87 and r = 0.53, in Ottawa 1999 and 2000, and Pergamino 2003 and 2004, respectively). Populations ARZM 01107, ARZM 07138, ARZM 10041, ARZM 13031, ARZM 16002 and Pora INTA exhibited the highest and most stable resistance to both species. Considering that disease resistance exhibited low specificity to the environment and to the fungal species in evaluations conducted in a wide range of environments and with fungal isolates collected from different hemispheres, the most resistant populations are potential sources of genes for stable resistance to these Fusarium spp.     

Increasing resistance to Fusarium crown and root rot in asparagus by gametophyte selection

In garden asparagus, Fusarium crown and root rot is the main cause of crop decline. Since chemical treatments are inefficient, efforts should focus on the development of resistant cultivars to control the disease. Toxic culture filtrate (TCF) of F. oxysporum has affected asparagus pollen germination and tube growth. Consequently, gametophyte selection was evaluated to ascertain if the application of selective agents at this level could increase selection efficiency. Two susceptible pistillate plants and one tolerant and one susceptible staminate plants were used in controlled crosses. Before pollination, a drop of a germination vehicle with TCF or without it was applied to the stigmas. Some pollinated pistils were fixed and analyzed by fluorescence microscopy; the rest were left on the plant for seed production. Fifty to 200 seeds were obtained per treatment combination (staminate plant x pistillate plant x pollination vehicle). The derived plantlets were inoculated in vitroand evaluated for disease symptoms. The application of TCF to stigmas reduced pollen germination and tube growth compared with untreated controls,regardless of the genotypic combination. Pollen germination and tube growth was poorer for the tolerant staminate genotype than for the susceptible one. When the TCF was applied, the number of seeds per pollination in comparison with the controls diminished only when the susceptible genotype was the pollinator. The percentage of affected root area of the progenies obtained after applying the TCF was lower than in the controls only when the tolerant genotype was the pollinator. Increasing Fusarium resistance in asparagus by means of gametophyte selection seems feasible. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic variation for head blight resistance in triticale caused by Fusarium graminearum isolates of different deoxynivalenol production

Summary Fusarium head blight infection causes severe yield losses and contamination of the grain with mycotoxins in triticale (× Triticosecale Wittmack) grown in temperate and semihumid areas. In a two-year experiment thirty-six genotypes were inoculated separately with two isolates of Fusarium graminearum differing fivefold in their in vitro deoxynivalenol (DON) production and the effect on various traits was studied. All traits were significantly affected by head blight. The two isolates differed considerably in their aggressiveness resulting in a mean reduction of grain weight per spike of almost 25% and 50%, respectively. Inter-annual correlation was high for average disease rating (r=0.63, P<-0.01) and low for the other traits. Therefore, disease rating, averaged from two to three records, was regarded a suitable criterion for screening purposes. The effect of isolates on genotypes was not stable over years. The mean DON content of five genotypes with diverse resistance levels was 68 mg kg^-1. In vitro DON production of the two isolates used for inoculation did not correspond to their aggressiveness and DON contamination of the grain.     

Genetic analysis of resistance to Fusarium head blight caused by Fusarium graminearum in Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165

The genetic constitution of resistance to Fusarium head blight (FHB, scab) caused by Fusarium graminearum in the Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165 was investigated using doubled haploid lines (DHLs) and recombinant inbred lines (RILs). Frequency distributions of DHLs derived from two F₁ crosses, Sumai 3 (very resistant to resistant; VR-R) / Gamenya (very susceptible; VS) and Sumai 3 / Emblem (VS), fitted well to 1: 2: 1 (resistant: moderately resistant: susceptible) ratios for reaction to FHB in the field. It is suggested that the resistance of Sumai 3 is controlled by two major genes with additive effects. One of the resistance genes may be linked in repulsion to the dominant suppressor B1 for awnedness with recombination values 15.1 ± 3.3% in Sumai 3 /Gamenya and 21.4 ± 4.3% in Sumai 3 / Emblem. Saikai 165 is a Japanese resistant line derived from an F₁ Sumai 3 / Asakaze-komugi (moderately resistant; MR). The data for RILs derived from the cross Emblem / Saikai 165, indicates that three resistance genes control the resistance of Saikai 165. This revised version was published online in July 2006 with corrections to the Cover Date.     

玉米拟轮枝镰孢菌穗腐病抗性基因的挖掘

玉米穗腐病是一种严重危害玉米生产的真菌性病害,而目前在世界范围内玉米育种上应用的大多数自交系缺少对穗腐病的抗性。玉米穗腐病抗性位点的挖掘和抗病基因的克隆,对玉米穗腐病的遗传改良至关重要。本研究旨在通过转录组测序和全基因组关联分析的方法进行玉米拟轮枝镰孢菌穗腐病抗性位点的挖掘并初步确定候选基因。抗病自交系法A和感病自交系掖81162的转录组测序结果表明,人工接种拟轮枝镰孢菌后7d两个自交系的差异表达基因有10,761个。通过全基因组关联分析共检测到5个与穗腐病抗性显著相关的SNP,这些SNP分布在1号和9号染色体上。通过比对B73 RefGen_v3并注释,发现SNP位点附近涉及的基因包括酰基激活酶1过氧化物酶体、蛋白磷酸酶2C 48、镁转运蛋白、受体蛋白激酶CRINKLY4和锌指CCCH域蛋白19。将在转录组测序中获得差异表达基因和全基因组选择中关联到的基因进行比对,发现全基因组关联分析中关联到的锌指CCCH域蛋白19同时也是转录组测序中获得的差异表达基因,表明锌指CCCH域蛋白19可能与玉米拟轮枝镰孢菌穗腐病的抗性相关。本研究结果不仅能为抗病基因的克隆和玉米的抗病...     

Genetic analysis of inbred lines and their crosses for resistance to head blight (Fusarium culmorum,F. graminearum) in winter rye

Summary For genetic analysis of head blight in winter rye (Secale cereale) caused by Fusarium culmorum, six homozygous inbred lines from the Petkus gene pool were crossed in all combinations to obtain 15 diallel F₁ crosses and the corresponding 15 F₂ crosses. These materials and 10 additional inbreds were artificially inoculated in a 2-year field experiment. The inbreds were also tested with F. graminearum in a separate sub-experiment.Single disease rating, average disease rating, and yield components (grain-weight per spike, 1000-grain weight, kernel number per spike) relative to the non-inoculated treatment were significantly affected by Fusarium head blight in all material groups. The relative grain weight per spike ranged from 26% to 88%. Significant genotypic and genotype x year interaction variances were found throughout. Heritabilities were highest for homogeneous inbreds (h²=0.6–0.8) and lowest for heterogeneous F₂ crosses (h²=0.4–0.6). Disease rating and relative grain-weight per spike were highly correlated for the inbreds and F₂ crosses (r0.7, P0.01), but lower for the F₁ crosses (r0.6, P0.05). Inter-annual correlation coefficients for disease ratings and relative grain-weight per spike ranged from r0.7 (inbreds) to r0.5 (F₂ crosses). The diallel analysis showed significant GCA effects only for relative 1000-grain weight in 1990, but significant SCA and SCAx year interaction variances for most traits. The resistances of 16 inbreds to F. culmorum and F. graminearum were tightly associated for all traits (r=0.96–0.97, P0.01).In conclusion, only slow progress can be expected from selecting for Fusarium head blight resistance in rye due to the limited amount of additive genetic variance and the great improtance of environmental factors.     

玉米对镰刀菌茎腐病抗性的生化反应

在抽雄期用禾谷镰刀菌孢子悬浮液接种抗病品种陕单931和感病品种西农11号,于接种后测定茎秆髓部组织内苯丙氨酸解氨酶、过氧化物酶活性变化、木质素和绿原酸的变化。结果表明,玉米植株受镰刀菌侵染后,抗病品种的苯丙氨酸解氨酶酶活上升快,活性强,且形成两个活性高峰,高活性时间持续长;感病品种苯丙氨酸解氨酶酶活上升慢,活性相对较弱,且只形成一个峰,高活性持续时间短。抗病品种过氧化物酶酶活峰值高,感病品种过氧化物酶酶活峰值低,且抗病品种高酶活持续的时间长,感病品种高酶活持续的短。研究还表明,植株原生的木质素对玉米的抗性贡献不大,而诱导的木质素在玉米的抗病性中起着主导作用。同时,无论抗、感品种,其组织诱导提取液对镰刀菌都有一定的抑制作用。     

Variation for resistance to Fusarium head blight in spring barley

Fusarium head blight (FHB) is a fungal disease of barley and other cereals, causing substantial yield and quality losses, mainly due to the contamination of the harvest with mycotoxins. We aimed to evaluate genetic variation for resistance to FHB and its association with other plant characters in diverse barley germplasm in order to identify useful lines for resistance breeding. The 143 barley lines consisted of 88 current European spring barley lines and cultivars, 33 accessions from the genebank at IPK Gatersleben, and 22 lines obtained from North American institutions. We conducted artificially inoculated field experiments with Fusarium graminearum Schwabe during two seasons. FHB severity was evaluated by repeated assessment of visual symptoms. On a set of 49 lines several trichothecene mycotoxins were analyzed. Variation for FHB severity was quantitative. The lines with lowest FHB severity were 'CIho 4196' and 'PI 566203'. Also within the European spring barley collection variation for FHB severity was highly significant. There was a significant negative correlation between plant height and FHB severity (r=– 0.55). FHB severity assessed in the field and the amount of deoxynivalenol in the harvested grains were positively correlated (r= 0.87). Several lines with a useful level of FHB resistance were found or confirmed and are recommended as crossing partners.     

Genetic variation for resistance to Fusarium head blight in bread wheat

Summary During a four year period, a total of 258 winter and spring wheat genotypes were evaluated for resistance to head blight after inoculation with Fusarium culmorum strain IPO 39-01. It was concluded that genetic variation for resistance is very large. Spring wheat genotypes which had been reported to be resistant to head blight caused by Fusarium graminearum were also resistant to F. culmorum. The resistant germplasm was divided into three gene pools: winter wheats from Eastern Europe, spring wheats from China/Japan and spring wheats from Brazil. In 32 winter wheat genotypes in 1987, and 54 winter wheat genotypes in 1989, the percentage yield reduction depended on the square root of percentage head blight with an average regression coefficient of 6.6. Heritability estimates indicated that for selection for Fusarium head blight resistance, visually assessed head blight was a better selection criterion than yield reduction.     

Fusarium ear rot and how to screen for resistance in open pollinated maize in the Andean regions

Ears infected with ear rot were collected from five provinces in Ecuador. Of the 44 samples analysed 26 carried Fusarium verticillioides, 11 F. subglutinans, two F. graminearum and five carried fungi different from Fusarium. The pathogenicity of ten isolates, seven of F. verticillioides and three of F. subglutinans, were tested. Per isolate 30 ears of the susceptible cultivar Mishca were inoculated by pricking a steel pin, dipped into a spore suspension, through the husks in the central part of the ear 14 days after mid-silk. Ears inoculated with sterile water and ears without any treatment, natural infection, served as controls. The disease severity (DS) of the ears ranged from 14 to 58% ear rot, the range being similar for both species. The DS of the water control, 19%, was much higher than that of the natural control of 2%. Five strains gave a DS of over 40%, significantly higher than the water control. The DS of the others were similar to the water control. In a series of experiments the effect of various methods of applying Fusarium spores through the husks into young ears were compared. All tested methods resulted in DSs significantly higher than those of the two controls. Inoculation with tooth picks and steel pins dipped in a spore suspension gave similar ear rot percentages. Inoculations at 7 to 14 days after mid-silk produced the highest DS’s. There was no significant effect of spore concentration on the DS. Cultivars differed considerably, the range being from around 20% to over 50%. Surprisingly, only wounding the husks, the sterile water control, resulted in a fairly high DS, much higher than that of the natural control. As the ranking order of the cultivars after wounding only and after inoculation did not seem to be different from the ranking order of the natural control it is suggested to use in areas with high inoculum pressures like the Andes only wounding by means of a steel pin for screening for resistance to maize ear rot.     

Crown depth and susceptibility to crown rot in wheat

Sources of partial resistance to crown rot caused by Fusarium pseudograminearum are detected in mature plants grown in artificially inoculated soil in the field. The resistance in most but not all of these sources can also be detected in seedlings. In order to determine whether partial resistance is related to depth of crown formation, this character was measured in 13 cultivars/lines with a range of reaction to crown rot. It was also measured in doubled haploid plants from the cross, Batavia/2–49. Crown depths varied from 17.1 mm to -2.3 mm (above ground) in pots in a waterbath at 25 ^°C and from 43.5 mm to 20.7 mm when plants were grown in the field. The correlation coefficient between relative susceptibility to crown rot (Field test) and crown depth of 13 cultivars/lines was 0.57 (p ≤ 0.05). With the exception of the cultivars, Sunco and Pelsart, partial resistance to crown rot was inversely related to depth of crown formation. This indicates that depth of crown formation may be partly responsible for the reaction of a cultivar/line to crown rot. Depth of crown formation was also measured in susceptible and partially resistant cultivars/lines grown from seed planted at different depths. As depth of seeding increased, depth of crown formation in partially resistant and susceptible cultivars/lines increased in similar proportions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Breeding and genetics of Fusarium basal rot resistance in onion

Fusarium basal plate rot (FBR), caused by Fusarium oxysporum f. sp. cepae, is an important soil-borne disease of onions worldwide. The causal organism infects the basal stem plate of the bulb and eventually kills the entire plant through degradation of the basal plate. F. o. f. sp.cepae infections in dormant bulbs during storage allow secondary infections to occur. The primary method of infection by F. o. f. sp. cepaeis through direct penetration of the basal stem plate. Infection can also occur through wounded tissue particularly roots and basal portions of bulb scales. The most cost-effective methods of control are crop rotation and host plant resistance. Current research suggests that a single gene, two genes, or multiple genes govern resistance to FBR. Breeding programs have successfully used screening procedures to develop intermediate- and long-day, FBR-resistant cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation for resistance to head blight caused by Fusarium graminearum in wild emmer (Triticum dicoccoides) originating from Israel

Head blight of wheat (FHB, scab) caused by Fusarium spp. has been associated with yield and quality losses in many wheat-growing regions. In tetraploid wheat sources of resistance are scarce. In the search for novel sources of resistance, 151 Triticum dicoccoides genotypes, originating from 16 habitats in Israel and one habitat in Turkey together with several control genotypes, were evaluated for reaction to fungal spread (Type II resistance) in replicated greenhouse experiments. Significant genetic diversity was found among the tested genotypes, the broad sense heritability for Type II FHB resistance was 0.71. Most of the tetraploid accessions were highly susceptible, only a few showed moderate resistance. Among the eight T. dicoccoides lines with the lowest relative infection rates, five originated from the Mt. Gerizim population, and three from the Mt. Hermon population. None of the T. dicoccoides lines reached the level of resistance present in the common wheat cultivar Sumai3. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics and population improvement of resistance to bacterial soft rot in Chinese cabbage

Resistance to bacterial soft rot caused by Erwinia carotovora subsp. carotovora is a quantitative trait. The narrow-sense heritability was from 42% to 60% in the studied populations. Griffing's diallel analysis and generation mean analysis indicated that additive genetic effects were most significant, and the resistant sources involved in this study appeared to have different genes or alleles. Recurrent phenotypic selection was used for improving the resistance level by combining different resistance genes from the selected genotypes of Chinese cabbage. After 3 cycles of recurrent selection, the level of resistance increased markedly. When the cycle 3 population was compared with the cycle 0 population, the mean disease severity rating was reduced 38% from 6.3 to 3.9, and the percentage of plant survival increased from 65% to 97% based on the mean of two years experiments using mist-chamber seedling inoculation methods. The improvement of resistance was also demonstrated in field assays. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation for maize root architecture in response to drought stress at the seedling stage

Although the root system is indispensable for absorption of nutrients and water, it is poorly studied in maize owing to the difficulties of direct measurement of roots. Here, 103 maize lines were used to compare root architectures under well-watered and water-stressed conditions. Significant genetic variation, with medium to high heritability and significant correlations, was observed for root traits. Total root length (TRL) and total root surface area (TSA) had high phenotypical diversity, and TRL was positively correlated with TSA, root volume, and root forks. The first two principal components explained 94.01% and 91.15% of total root variation in well-watered and water-stressed conditions, respectively. Thus, TRL and TSA, major contributors to root variation, can be used as favorable selection criteria at the seedling stage. We found that stiff stalk and non-stiff stalk groups (temperate backgrounds) showed relatively higher mean values for root morphological diversity than the TST group (tropical/subtropical background). Of the tested lines, 7, 42, 45, and 9 were classified as drought sensitive, moderately sensitive, moderately drought tolerant, and highly drought tolerant, respectively. Seven of the 9 extremely drought tolerant lines were from the TST group, suggesting that TST germplasms harbor valuable genetic resources for drought tolerance that could be used in breeding to improve abiotic stress tolerance in maize.     

Screening for Fusarium resistance in seedling populations of Asiatic hybrid lily

A test to select Fusarium resistant seedlings of the Asiatic hybrid lily is described. Young seedlings of 28 populations, obtained from an incomplete diallel between eight parents with different levels of Fusarium resistance, were tested for resistance. Significant differences in Fusarium resistance between and within populations were detected. The average percentage of selected seedlings ranged from 34% in resistant × resistant crosses to 2% in susceptible × susceptible crosses. Although resistant descendants were obtained in susceptible × susceptible crosses, using at least one resistant parent produced higher percentages of resistant seedlings. The resistance level of the parents correlated highly with the general combining ability for Fusarium resistance based on the seedling test. For eight populations, seedlings selected for Fusarium resistance and non-tested (control) seedlings of the same cross were compared, after propagation, in a clonal test. Variation between and within populations, found at seedling level, was confirmed at clonal level. A positive selection response was found for all eight populations. In the seedling test, approximately 18% of the seedlings were selected as resistant of which 15% (2.7% of seedlings tested) appeared to be susceptible escapes. Comparison between selection at seedling level and at clonal level indicated that approximately 25% of the seedlings tested were missed (rejected resistant plants) in the seedling test. The practical use of a seedling test for Fusarium resistance in lily breeding programs is discussed.     

Effect of row type,flowering type and several other spike characters on resistance to Fusarium head blight in barley

Fusarium head blight (FHB) is a destructive disease of barley. The genetics and expression of resistance to FHB in barley is complex, and various spike characters are thought to possibly influence resistance. Tests using spray-inoculation of Fusarium graminearum at anthesis in greenhouse environments showed that two-rowed and cleistogamous varieties from Japan belong to the highest resistance group, while six-rowed and chasmogamous varieties are mostly susceptible. In order to evaluate the effect of such spike characters, including row type and flowering type, on FHB resistance, near-isogenic lines (NILs) differing in these characters were tested for their resistance. Two testing methods were used: the pot-plant and cut-spike methods, in which spikes at anthesis were spray-inoculated in greenhouse environments. The chasmogamous NILs and some six-rowed NILs were significantly more diseased than cleistogamous and two-rowed parent lines, respectively, and the difference in FHB severity was greater and more stable between cleistogamous/chasmogamous NIL pairs than between two-/six-rowed pairs. Slight or no differences were observed in glaucous/non-glaucous, normal/dense spike, normal/uzu type and normal/deficiens NIL pairs. The results indicate that the contribution of cleistogamy and/or the genetic background toward FHB resistance is more than that of row type and the other tested spike characters. Further, it should be possible to develop six-rowed varieties with FHB resistance nearly as good as that of the two-rowed varieties.     

Diallel analysis of resistance to head blight caused by Fusarium culmorum in winter wheat

Summary Ten homozygous winter wheat genotypes representing different levels of resistance to Fusarium head blight were crossed in all possible combinations excluding reciprocals. Parents, F₁ and F₂ were inoculated with one pathogenic strain of Fusarium culmorum. Data for head blight, observed 21 days after first inoculation (OBS-2), and for the area under the disease progress curve, based on observations 14, 21 and 28 days after first inoculation (AUDPC), were analyzed. The contrast between parents and F₁ crosses indicated dommance effects of the resistance genes. Diallel analysis according to Griffing's Method 4, Model 1 showed significant general combining ability (GCA) effects for both F₁ and F₂; specific combining ability effects were not significant. With the exception of one genotype for which general performance for Fusarium resistance was not in agreement with its GCA, the resistance to F. culmorum was uniformly transmitted to all offspring, and the parents can be described in terms of GCA. It is suggested that in the progenies with one of the awned lines as parent, one resistance gene was linked with the gene coding for presence of awns, located on chromosome 4B. A single observation date, taken at the right time, was as effective in assessing resistance as the AUDPC.