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.     

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.     

Identification of RAPD markers linked to fusarium crown and root rot resistance (Frl) in tomato

In tomato ( Lycopersicon esculentum Mill.) a single dominant gene ( Frl) on chromosome 9 confers resistance to fusarium crown and root rot (crown rot) incited by Fusarium oxysporum f. sp. radicis-lycopersici. To identify randomly amplified polymorphic DNA (RAPD) markers linked to Frl, crown rot susceptible and resistant tomato lines were screened for polymorphisms using 1000 random 10-mer primers and three reliable RAPD markers were found linked to Frl (UBC #'s 116, 194, and 655). A codominant polymorphic PCR marker of TG101, a restriction fragment length polymorphic (RFLP) marker linked to Frl, was developed to facilitate the linkage studies. Using TG101 and the four RAPD markers, on a Frl segregating backcross population of 950 plants indicated that all belong to the same linkage group. The polymorphic allele order was found to be TG101 – 655 – 116 – 194 – Frl. UBC 194 was found to be 5.1 cM from Frl in this population. Furthermore, it was the only marker found in the resistant genotypes ‘Mocis’ and Fla 7226, whereas resistant genotypes ‘Momor’, Ohio 89-1, and Fla 7464 all had UBC 194 and UBC #'s 116, 194, and 655. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic and statistical models for estimating genetic parameters of maize seedling resistance to Fusarium graminearum Schwabe root rot

Root lodging is an important problem in corn fields. Fungi recovered from roots include seedling blight and stalk rot pathogens. The objective of this work was to study the inheritance of maize seedling resistance to pathogens causing maize lodging. The Fusarium graminearum strain, 241 Fr1, was isolated from maize lodged plants and identified as the most pathogenic isolate for root rotting. Nine inbred lines of maize and their diallel F₁ crosses plus control genotypes were studied. Seedlings were inoculated at the stage of four-leaves. Disease severity was measured as percentage of the root rotted area. Highly significant differences between inoculated and non-inoculated genotypes were found. Four genetic models and two statistical approaches—the mixed model for the best linear unbiased prediction (BLUP) and the general linear model (GLM)—were used for the analysis. Favorable heterosis of resistance of hybrids over inbreds was the most important effect detected. The general combining ability (GCA) effects were significant for all genetic models and statistical methods studied, and a good agreement existed among the GCA estimates by the different methods. The type of gene action, either additive or dominance, showed a large variation among the parental inbreds and hybrids. Selection of additive effects based exclusively on inbred lines is not sufficient to confer resistance to hybrids, additional selection should be practiced on hybrids to look for favorable dominance effects. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

Monogenic resistance in tomato to Fusarium oxysporum f. sp. lycopersici race 3

Summary Resistance to fusarium wilt, incited by Fusarium oxysporum (Schlecht.) f. sp. lycopersici (Sacc.) Snyder & Hansen race 3 in tomato (Lycopersicon esculentum Mill.) was discovered in LA 716, a L. pennellii accession. A resistant BC₁F₃ breeding line, E427, was developed from LA 716. E427 was crossed with the susceptible cv. Suncoast and F₁, BCP₁, BCP₂ (to Fla 7155, a susceptible parent) F₂, F₃, and BCP₂S₁ seeds were obtained. Segregation for resistance following root dip inoculation over three experiments indicated a single dominant gene controlled resistance. Five of the 12 BCP₁S₁'s segregated more susceptible plants, whereas one of the 12 segregated more resistant plants than expected (P<0.05). Three of 23 F₃ lines segregated more susceptible plants than expected while 1 of the 23 had more resistant plants than expected (P<0.05). Segregation in all other lines fit expected ratios. Five of the 23 F₃'s were homozygous resistant which was an acceptable fit to expectations (P=0.1–0.5). The gene symbol I ₃ is proposed for resistance to race 3 of the wilt pathogen. Deviations from expected ratios in data reported here and for other breeding lines indicate an effect of modifier genes and/or incomplete penetrance. Plant age at inoculation and seed dormancy did not affect results.Florida Agricultural Experiment Station Journal Series No. 8101.     

The in vitro phytotoxicity of culture filtrates of Fusarium oxysporum to five genotypes of Amaranthus hybridus

Stem decay and root rot of Amaranthus hybridus, caused by Fusarium oxysporum is a serious threat to the commercial production of this crop in South Africa. Five Amaranthus hybridus varieties were examined in vitro for sensitivity to a culture filtrate of Fusarium oxysporum. The phytotoxicity of the culture filtrate was assessed for its inhibitory effect on callus and seeding root growth, as well as on the viability of callus cells. The five varieties exhibited a significant amount of variation in response to the culture filtrate of the pathogen. Variety 17 was the most sensitive variety in each bioassay, whereas variety 20 displayed least sensitivity to the culture filtrate. Callus of variety 20 grew well in the presence of concentrations of culture filtrate that were toxic to another four varieties and the percentage mortality of callus cells after exposure to the filtrate was also the lowest of the five varieties. Root growth of variety 20 was also least affected by exposure to the culture filtrate for up to 6 days. To our knowledge, the presence of resistance in germplasm of A. hybridus to culture filtrates of F. oxysporum has not been demonstrated before. The present study is therefore of significant value to breeding programs aimed at speedily finding amaranth cultivars that are resistant to this important pathogen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fusarium wilt of chickpea: physiological specialization, genetics of resistance and resistance gene tagging

Chickpea wilt caused by Fusarium oxysporum f. sp. ciceris is one of the major yield limiting factors in chickpea. The disease causes 10–90% yield losses annually in chickpea. Eight physiological races of the pathogen (0, 1A, 1B/C, 2, 3, 4, 5 and 6) are reported so far whereas additional races are suspected from India. The distribution pattern of these races in different parts of the world indicates regional specificity for their occurrence leading to the perception that F. oxysporum f. sp. ciceris evolved independently in different regions. Pathogen isolates also exhibit differences in disease symptoms. Races 0 and 1B/C cause yellowing syndrome whereas 1A, 2, 3, 4, 5 and 6 lead to wilting syndrome. Genetics of resistance to two races (1B/C and 6) is yet to be determined, however, for other races resistance is governed either by monogenes or oligogenes. The individual genes of oligogenic resistance mechanism delay onset of disease symptoms, a phenomenon called as late wilting. Slow wilting, i.e., slow development of disease after onset of disease symptoms also occurs in reaction to pathogen; however, its genetics are not known. Mapping of wilt resistance genes in chickpea is difficult because of minimal polymorphism; however, it has been facilitated to great extent by the development of sequence tagged microsatellite site (STMS) markers that have revealed significant interspecific and intraspecific polymorphism. Markers linked to six genes governing resistance to six races (0, 1A, 2, 3, 4 and 5) of the pathogen have been identified and their position on chickpea linkage maps elucidated. These genes lie in two separate clusters on two different chickpea linkage groups. While the gene for resistance to race 0 is situated on LG 5 of Winter et al. (Theoretical and Applied Genetics 101:1155–1163, 2000) those governing resistance to races 1A, 2, 3, 4 and 5 spanned a region of 8.2 cM on LG 2. The cluster of five resistance genes was further subdivided into two sub clusters of 2.8 cM and 2.0 cM, respectively. Map-based cloning can be used to isolate the six genes mapped so far; however, the region containing these genes needs additional markers to facilitate their isolation. Cloning of wilt resistance genes is desirable to study their evolution, mechanisms of resistance and their exploitation in wilt resistance breeding and wilt management.     

Potential of a Fusarium eumartii culture filtrate on the screening for wilting resistance in potato

Summary Fusarium solani f.sp. eumartii Carp. Snyder and Hansen (Fusarium eumartii) is a soil inhabitant that induces the so-called Potato Wilt and Stem End Rot disease. Prior to wilting, the pathogen induces peculiar small bronze spots on the leaflets. Failure to isolate F. eumartii from infected leaflets suggests the involvement of a toxin in the disease. The fungus was grown in liquid Richard's medium and thereafter a filtrate was obtained dialyzing (MW cutoff 12,000–14,000) and sterilizing the culture by filtration (0.22 m). Potato leaves treated with both the pathogen or the filtrate showed symptoms of bronze spots and significantly higher electrolyte leakage when compared to controls. Tomato leaves showed neither bronze spots nor electrolyte leakage after plant inoculation with the pathogen or with the filtrate treatment. Both, the absence of visible symptoms and the lack of electrolyte leakage in tomato could be associated to a certain degree of host specificity of the F. eumartii filtrate towards potato. The filtrate also induced symptoms similar to infections by F. eumartii in adult plants and in vitro plantlets of cultivars Huinkul MAG and Kennebec. Callus responses to the filtrate were related to responses of the cultivars to the pathogen in greenhouse. These results show the potential of the culture filtrate of F. eumartii for use in screening for wilting resistance.     

Resistance to Fusarium crown rot in wheat and barley: a review

Fusarium crown rot (FCR) is becoming a major disease in many parts of the cereal‐growing regions worldwide. Significant QTL conferring FCR resistance have been reported on 13 of the 21 possible hexaploid wheat chromosomes in wheat and on three of the seven chromosomes in barley. Available results show that host resistance to FCR is not pathogen species‐specific, that resistance QTL have strong additive effect and that both plant height and growth rate affect FCR severity. Further, different loci seem to be responsible for resistances to FCR and Fusarium head blight although both diseases can be caused by the same Fusarium pathogens. Although marker‐assisted selection for FCR resistance has been initiated, the available markers are all derived from QTL mapping, which provides only limited resolution. Further work has to be conducted in developing diagnostic markers before significant progress can be made in deploying marker‐assisted selection as a routine tool to accelerate and improve FCR in breeding programmes.     

Localization ability,latent period and wilting rate in eleven carnation cultivars with partial resistance to Fusarium wilt

Summary The latent periods, wilting rates and percentages of diseased plants were analyzed for 11 carnation cultivars after root and after stem inoculation with race 2 of Fusarium oxysporum f.sp. dianth. There was no conclusive evidence for the presence of an independent extravascular resistance mechanism, except for Lena plants in which, additional to the vascular resistance components, independent root-bound factors causing retardation of the colonization and wilting process were found. A large variation was observed in the ablity of the cultivars to localize the pathogen in the vascular tissue shortly after infection of the xylem. This ability was positively correlated with the latent period, and negatively with the wilting rate and final disease index. In resistant cultivars, secondary compartmentalization of the fungus higher up in the stem was also observed. After stem inoculation, differences among the cultivars in localization ability and wilt-retarding actors could be identified at an early stage by comparing the precentages of non-colonized plants or the percentages of plants lacking vascular discolouration.     

Development of molecular markers linked to the <Emphasis Type="Italic">Fom-1</Emphasis> locus for resistance to Fusarium race 2 in melon

Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis (F.o.m), is a worldwide soil-borne disease of melon (Cucumis melo L.). The most effective control measure available is the use of resistant varieties. Resistance to races 0 and 2 of this fungal pathogen is conditioned by the dominant gene Fom-1. An F₂ population derived from the ‘Charentais-Fom1’ × ‘TRG-1551’ cross was used in combination with bulked segregant analysis utilizing the random amplified polymorphic DNA (RAPD) markers, in order to develop molecular markers linked to the locus Fom-1. Four hundred decamer primers were screened to identify three RAPD markers (B17₆₄₉, V01₅₇₈, and V06₁₀₉₂) linked to Fom-1 locus. Fragments amplified by primers B17₆₄₉ and V01₅₇₈ were linked in coupling phase to Fom1, at 3.5 and 4 cM respectively, whereas V06₁₀₉₂ marker was linked in repulsion to the same dominant resistant allele at 15.1 cM from the Fom-1 locus. These RAPDs were cloned and sequenced in order to design primers that would amplify only the target fragment. The derived sequence characterized amplified region (SCAR) markers SB17₆₄₅ and SV01₅₇₄ (645 and 574 bp, respectively) were present only in the resistant parent. The SV06₁₀₉₂ marker amplified a band of 1092 bp only in the susceptible parent. These markers are more universal than the CAPS markers developed by Brotman et al. (Theor Appl Genet 10:337–345, 2005). The analysis of 24 melon accessions, representing several melon types, with these markers revealed that different melon types behaved differently with the developed markers supporting the theory of multiple, independent origins of resistance to races 0 and 2 of F.o.m.     

Morphological and molecular characterization of melon accessions resistant to Fusarium wilts

Fusarium wilt incited by Fusarium oxysporum f. sp. melonis (F.o.m) is one of the most widespread and devastating melon diseases. While resistance to physiological races 0, 1, and 2 is relatively frequent in different botanical varieties, sources of resistance to race 1,2 are restricted to a few Far-Eastern accessions. In this work, the results of a screening for resistance to F.o.m. race 1,2 among 32 accessions are presented. Three Japanese accessions (‘Kogane Nashi Makuwa’, ‘C-211’, and ‘C-40’) showed the highest resistance levels, but useful levels of resistance were also detected in one Russian ‘C-160’ and two Spanish (‘C-300’ and ‘Mollerusa-7’) accessions. These resistant materials, together with other accessions previously described as resistant to F.o.m. races 0, 1, and/or 2 have been morphologically and molecularly characterized. Based on cluster analysis, these accessions have been grouped according to the botanical subspecies they belong to. Assessment of genetic diversity indicated that the resistant accessions to races 0, 1 and 2, are scattered along the established clusters. On the other hand, high levels of resistance to the race 1,2 could be found only among accessions belonging to Cucumis melo subsp. agrestis, nevertheless, a certain degree of resistance to this race could also be found within some accessions belonging to subsp. melo. As far as we know, this is the first report of resistance to F.o.m race 1,2 found out from the Far-Eastern melon material. Based on fruits characteristics, it appears that several inodurus and cantalupensis accessions could be exploited in breeding programs as resistance sources to F.o.m races 0, 1 and/or 2 for the improvement of these melon types. The accessions with the highest levels of resistance to the race 1,2 appeared to be very distant both molecularly and morphologically from the commercial types. Nevertheless ‘C-160’, ‘C-300’, and ‘Mollerusa-7’ classified as var. inodorus are morphologically very similar to the Spanish commercial types and might be used as resistant sources in breeding these melon types.     

Assessment of Gossypium sturtianum and G. australe as potential sources of Fusarium wilt resistance to cotton

When challenged with Fusarium oxysporum f. sp. vasinfectum (Fov) from vegetative compatibility groups (VCGs) 01111 and 01112 in glasshouse tests, Gossypium australe Mueller and Gossypium sturtianum Willis accessions showed a variety of disease responses ranging from highly resistant to highly susceptible. Under high disease pressure G. sturtianum accession Gos-5275 was significantly more resistant than the commercial G. hirsutum cultivars that are designated standards for Fusarium resistance by Australian cotton breeders. Under low disease pressure G. sturtianum accession Gos-5250 was more susceptible than a highly susceptible commercial cultivar. A series of glasshouse tests was performed at two locations (Indooroopilly, QLD. and Canberra, ACT), and under low and high disease pressure. In these tests, a hexaploid cross (Gos-5271) generated from a Fusarium-resistant G. sturtianum (Gos-5275) and a Fusarium-susceptible G. hirsutum L. (CPI-138969) was significantly more resistant to Fusarium wilt than its G. hirsutum parent. Thus G. sturtianum, with a diploid genome and a range of responses to Fov challenge, has the potential to provide the basis for the elucidation of the genetic basis of resistance to Fusarium wilt in cotton species. In addition, resistant accessions of G. sturtianum are identified as a potential source of Fusarium wilt resistance genes for cotton breeding. In the glasshouse tests used to assess the resistance of various Gossypium accessions to Fusarium wilt disease, the scoring of vascular browning was found to give a more reliable indication of disease severity than the scoring of foliar symptoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selection parameters for resistance to Fusarium oxysporum f. sp. cubense race 1 and race 4 on diploid banana (Musa acuminata Colla)

Summary Shoot tip cultures from banana clones susceptible and resistant to Fusarium oxysporum f. sp. cubense (FOC) race 1 and race 4 were grown in vitro in the presence of different concentrations of fusaric acid and fungal crude filtrates or inoculated with a conidial suspension of FOC to assess correlation between in vivo and in vitro behaviour. Explants were susceptible to both filtrate and fusaric acid irrespective to their known field resistance/susceptibility response. No clear linkage between in vivo and in vitro behaviour was observed and our results suggest that the use of crude filtrate or non-host specific toxin (fusaric acid) in a screening programme for selecting a novel resistant genotype of Musa to FOC is not feasible. When peroxidase activity was used as a parameter to discriminate between sesceptibility and tolerance, results were in good agreement with field response of host plant to pathogens. Early enzymatic activity increased in the incompatible host-pathogen interaction but not in the compatible interaction.Abbreviations IBA Indolebutyric acid - 2iP 6-dimethylallylamino-purine - VCG Vegetative Compatibility Group - FOC Fusarium oxysporum f. sp. cubense - IEF isoelectrofocusing     

Breeding for resistance to Fusarium oxysporum f. sp. Tulipae in tulip (Tulipa L.). I. Development of a screening test for selection

Summary Fusarium oxysporum causes the most serious fungus disease in tulip. Breeding for resistant cultivars may considerably contribute to a solution of the problem.Bulbs of various cultivars planted in contaminated soil showed important and significant differences in resistance. Inoculation trials in the field and in the glasshouse have led to recommendations for the screening of juvenile and adult bulbs.     

The oat line Pc54 as a source of resistance to crown rust,stem rust and powdery mildew in Europe

Summary The oat line Pc54 was found to be resistant to powdery mildew under both field and glasshouse conditions. The ratio of resistant to susceptible F₂ and F₂ progeny of a cross between a selection from the Pc54 line (Cc7422) and a susceptible cultivar (Selma) showed that, in addition to carrying the crown rust resistance gene Pc54 and the pg15 gene for stem rust resistance, the mildew resistance of the Pc54 line was conditioned by a single incompletely dominant gene along with additional factors which modified the expression of resistance. Previous results, that there was no linkage between genes Pc54 and Pg15, were confirmed. In addition, there was no evidence of linkage between the mildew resistance gene and gene Pc54. Evaluation of selections from within the Pc54 line showed that the expression of both stem rust and mildew resistance was modified by, or linked to, plant height. The effectiveness of genes Pc54 and Pg15, as measured by virulence frequencies, in central and eastern Europe is described.     

Breeding for resistance to fusarium oxysporumF. SP. tulipae in tulip (tulipaL.).2. phenotypic and genotypic evaluation of cultivars

Summary Fusarium bulb rot is a serious tulip disease. Breeding for resistance may contribute considerably to a solution of the problem.It has been demonstrated that juvenile and adult bulbs of the same cultivars in Fusarium contaminated soil showed good agreement in degree of resistance.From an incomplete diallel cross of these cultivars second-year bulblets of 62 progenies were planted in both contaminated and non-contaminated soil. The percentages of non-diseased bulbs harvested provided a criterion for resistance. The analysis of combining ability for the degree of resistance revealed that both the mean square of GCA and that of SCA were significant. The relative magnitudes of the GCA and SCA mean squares suggest that resistance is governed primarily by additive gene action. The GCA of individual parents could be estimated and tested. In general it corresponded with their phenotypic behaviour.