Southern Rust Research Articles

Construction and characterization of a bacterial artificial chromosome library of the maize inbred line Qi319

Zea mays L. has been the most cultivated crop and the crop with the largest yield in China since 2012. We constructed a bacterial artificial chromosome (BAC) library for the maize inbred line Qi319, which may be used as a key source for disease-resistant maize breeding in China. The BAC contains 270,720 clones, with an average insert size of 90 kb. The coverage of the library is about 10.43 genome equivalents when considering a haploid genome size of 2300 Mb, providing a 99.99% likelihood of isolating any maize gene or sequence in the library. An average of 12 clones were obtained by polymerase chain reaction screening by using primer pairs linked to the genes for resistance to maize southern rust and rough dwarf. The results indicate that the library can satisfy the requirements for recovering specific sequences. The library is available to researchers to whom it may be of interest.

English

This study aimed to evaluate the effect of fungicide trifloxystrobin (200 g/L 20% m/v) + tebuconazole (100 g/L 10% m/v) at different phenological stages in controlling southern rust and Cercospora leaf spot in the maize crop and on its productivity. This work was carried out in 2013, Ertel farm, located in the city of Toledo – PR of Brasil. The experimental design was a randomized complete block in a factorial (2x4+1) with four replications. The treatments consisted of evaluating two diseases, Southern Rust and Cercospora leaf spot, and four phenological stages of fungicide application (V8, V10, VT and R1 of maize) with the presence of a control. The authors evaluated the disease incidence and severity, the Area Under Disease Progress Curve (AUDPC) and the fungicide control efficiency for foliar diseases were observed. In addition to this, some agronomic variables were also evaluated: plant height, ear insertion height, stem diameter, average diameter of ear, ear length, number of rows per ear, number of grains per row, number of grains per ear, thousand grain weight and productivity. The results showed no significant statistical difference for the variables evaluated, except for plant height. Based on these results, it can be concluded that the mixture of triazole with estrobirulina is feasible to control the severity of these diseases in maize, though it was not observed any statistical difference in the different treatments in relation to the average productivity. It is worth mentioning that the use of fungicide tends to provide greater sanity to plants and consequently it improves production rates. In general, the application of the fungicide in the pre-anthesis stage (VT) tends to exhibit better responses.   Key words: Zea mays L., Puccinia polysora, Cercospora zeae-maydis.

Geographic and genetic identification of RppS, a novel locus conferring broad resistance to southern corn rust disease in China

Southern corn rust, a devastating fungal disease of maize, can cause significant loss of grain yield during intermittent outbreak. Growing resistant varieties is the most cost-effective way to manage southern rust in field corn. However, the prevalence of incomplete resistance owing to rapid evolution of pathogen warrants the necessities of discovering new resistant resources. To this end, the disease occurrence of 15 maize inbred lines in response to southern rust was examined in fields located in tropical, subtropical and temperate regions respectively. Overall, the character of resistance or susceptibility was rather steady among locations for most of inbred lines although infrequent variations existed. A tropical inbred line, SCML205, displayed fully resistant response in all the locations tested. By contrast, Jing24, W1636, Zheng58, W541 and G10-2426 exhibited completely susceptible response. A 3:1 segregation ratio of resistance to susceptibility was identified in the progeny of F2 population generated from the cross of SCML205 × Jing24, demonstrating SCML205 harbors a single dominant resistant gene. Allelism test was performed to confirm the resistance conferred by a novel locus, which was designated as RppS. Genetic mapping were conducted to locate RppS to the distal arm of chromosome 10S, a region close to other resistant genes known so far. Together, our survey of the resistance to southern rust in numerous inbred lines leads to the identification of a novel resistant gene, which would be tremendously valuable for plant breeding.

Evaluation of maize inbred lines currently used in Chinese breeding programs for resistance to six foliar diseases

Foliar diseases are common in most maize-producing regions and have caused serious yield reduction in China. To evaluate genetic resistance of parental lines actively used in maize breeding programs to major foliar diseases, 152 maize inbred lines were tested against northern corn leaf blight (NCLB), southern corn leaf blight (SCLB), Curvularia leaf spot (CLS), gray leaf spot (GLS), common rust, and southern rust from 2003 to 2005. A small number of lines exhibited highly resistant reactions to common rust and southern rust, but none were highly resistant to NCLB, SCLB, CLS, and GLS. Although 53.3%, 40.8%, and 80.7% of lines were resistant to NCLB, SCLB, and common rust, the resistance in most lines was moderate. Resistance to CLS, GLS, and southern rust was rare in this collection of maize lines. Five lines, 313, Chang 7-2, Qi 319, Qi 318, and Shen 137, were resistant to five diseases tested. Lines belonging to heterotic subgroup PB exhibited better resistance to the foliar diseases than lines from other heterotic subgroups, such as BSSS, PA, Lancaster, LRC, and PA. The results will be of benefit to breeders for selecting lines in disease resistance breeding programs.

FTIR研究南方锈病侵染对玉米叶片中蛋白质和碳水化合物的影响

In order to study biochemical parameters of maize leaf,which infected by maize southern rust,Fourier transform infrared spectroscopy was applied to obtain the spectra of infection and normal maize leaves.The characteristic region and fingerprint region at spectrum were selected to study the change of protein and carbohydrate in maize leaf.Compared infection with normal leaf spectrum,amide bands had diversification obviously,the change of absorption band of carbohydrate was not prominence.It showed that the protein secondary structures had changed,and the diversification of carbohydrate in infection leaf was not obviously.Curve-fitting analysis of wave number at 1 800~1 480 presented the sheet and helix in protein secondary structures was decrease in infected leaf,and the turn structure was increase at the infected initial stage.The random coil structure was increase rapidly at infected end stage,this structure was absent at infected initial stage and normal maize leaves.The results show that Fourier transform infrared spectroscopy combine with curve-fitting analysis can be used to explore the change of biochemical parameters in infection maize leaf,which provides evidence for studying the disease resistance of maize.

Fine Mapping of RppP25, a Southern Rust Resistance Gene in Maize

Southern rust (Puccinia polysora Underw.) is a major disease that can cause severe yield losses in maize (Zea mays L.). In our previous study, a major gene RppP25 that confers resistance to southern rust was identified in inbred line P25. Here, we report the fine mapping and candidate gene analysis of RppP25 from the near-isogenic line F939, which harbors RppP25 in the genetic background of the susceptible inbred line F349. The inheritance of resistance to southern rust was investigated in the BC1 F1 and BC3 F1 populations, which were derived from a cross between F939 and F349 (as the recurrent parent). The 1:1 segregation ratio of resistance to susceptible plants in these two populations indicated that the resistance is controlled by a single dominant gene. Ten markers, including three simple sequence repeat (SSR) markers and seven insertion/deletion (InDel) markers, were developed in the RppP25 region. RppP25 was delimited to an interval between P091 and M271, with an estimated length of 40 kb based on the physical map of B73. In this region, a candidate gene was identified that was predicted to encode a putative nucleotide-binding site leucine-rich repeat (NBS-LRR) protein. Two co-segregated markers will aid in pyramiding diverse southern rust resistance alleles into elite materials, and thereby improve southern rust resistance worldwide.

Climatic changes and the potential future importance of maize diseases: a short review

This mini-review summarizes the existing knowledge and hypotheses on the potential changes to the future importance of maize diseases due to projected global climatic changes. In contrast to fungal pathogens, there is almost no information available on viral and bacterial diseases. Most studies related to fungi refer to Aspergillus and Fusarium species, which are causal agents of maize ear rot, and the related risk of mycotoxin contamination of maize grain, potentially harmful to animals and humans. Just a single long-term simulation study based on a modelling approach driven by a climate change scenario has been reported for a maize disease so far. It projects a reduced risk of Puccinia polysora (southern rust) occurrence in Brazil in this century. More simulation studies, ideally those which also generate quantitative disease-yield loss data for different maize diseases and locations are certainly needed in order to include the future potential disease risk in maize to the climate change debate. This will enable the estimation of the future maize productivity based on both abiotic factors such as temperature and biotic factors such as diseases. A fundamental conclusion of this mini-review is that global maize disease problems caused by a changing climate will probably not consistently worsen, because climatic changes may also improve the crop health situation in maize depending on the disease, location and time scale considered, although ear rots and associated mycotoxin contamination of maize grain are expected to increase in many countries worldwide. Reducing ear rot disease risk is already of high priority and will likely demand particular attention in the future as well.

Effect of treatment with a mixture of bacteria and fibrolytic enzymes on the quality and safety of corn silage infested with different levels of rust

This project aimed to determine if a dual-purpose bacterial inoculant could mitigate potential adverse effects of increasing levels of rust infestation on the quality, aerobic stability, and safety of corn silage. Corn plants with no rust infestation (NR), or medium (all leaves on the lower half of the plant affected, MR), or high (all leaves affected, HR) levels of southern rust infestation were harvested at random locations on a field, chopped, and ensiled without (control, CON) or with a dual-purpose inoculant applied at a rate that supplied 1×105cfu/g of Pediococcus pentosaceus 12455 and 4×105cfu/g of Lactobacillus buchneri 40788. Each treatment was prepared in quadruplicate in 20-L mini silos and ensiled for 97 d. As the level of rust infestation increased, the concentrations of dry matter (DM) and neutral detergent fiber increased, whereas DM digestibility decreased by up to 16%. Control HR silages also had lower 24-h neutral detergent fiber digestibility (NDFD; 36.2% of DM) than CON MR (39.8%) or NR silages (38.1%). Inoculation increased the NDFD of NR (43.4%) and MR silages (45.7%) but not HR silages (33.0%). Concentrations of lactate and volatile fatty acids decreased with increasing rust infestation in CON silages, but this trend was absent in inoculated silages. In HR silages, inoculation increased aerobic stability by 75% (77.3 vs. 44h), and prevented production of aflatoxin (5.2 vs. 0mg/kg). The concentration of aflatoxin in uninoculated HR silages exceeded action levels stipulated by the US Food and Drug Administration. In conclusion, increasing rust infestation was associated with reductions in the nutritive value and fermentation of corn silage. Inoculation reduced adverse effects of rust infestation on the fermentation, increased 24-h NDFD of NR and MR silages, and decreased aerobic spoilage and aflatoxin production in HR silages.

Diallel analysis of yield, popping expansion, and southern rust resistance in popcorn lines

Ten popcorn inbred lines were crossed in a circulant partial diallel matching scheme (group of lines derived from IAC 112 × group of lines from 'Zaeli'). The hybrids were evaluated in respect to grain yield (GY), popping expansion (PE), and resistance to southern rust (Puccinia polysora, Pp), in randomized block design, with three replications. Data was examined by analyses of variance and Kempthorne and Curnow's diallel analysis. General combining ability (GCA) was significant (p < 0.10) in the set 2-Zaeli for GY, PE, and partial resistance to Pp. This indicated that additive gene effects are predominant, and therefore breeding methods of recurrent selection are recommended. However, none of lines had outstanding GCA for GY and PE. The line P8.5 was recommended to form breeding populations for resistance to Pp. Specific combining ability (SCA) was detected for GY. The P9.24 × P8.6 might be promising for GY, if exploited using interpopulational breeding methods.

Genetic resistance of new popcorn hybrids to foliar diseases

The level of genetic resistance to foliar diseases in 54 new simple popcorn hybrids was evaluated in field conditions. Two trials in a randomized complete block design were conducted in the 2006/07 growing season. The disease intensity in genotypes was compared by the area under the disease progress curve, expressing the severity. Significant differences (P ≤ 0.01) of resistance to southern rust (Puccinia polysora) northern leaf blight (Exserohilum turcicum) and Phaeosphaeria leaf spot (complex Phaeosphaeria maydis / Pantoea ananas) were observed. The cluster analysis detected different resistance levels to the series of leaf diseases. In 12 of the new hybrids the resistance level to the set of diseases was similar as in the commercial hybrid IAC 112, considered the best reference for leaf disease resistance among commercial popcorn genotypes.

An Unusual Occurrence of Southern Rust, Caused by Rpp9-virulent Puccinia polysora, on Corn in Southwestern Georgia.

Southern rust, caused by Puccinia polysora Underw., occurs frequently on corn (Zea mays) grown in subtropical or tropical regions. When conditions are favorable, southern rust also occurs in temperate climates of the central and southern United States although the fungus does not survive on corn crop residue and must be introduced to temperate regions each growing season. Several single, dominant, resistance genes, designated as Rpp genes, convey hypersensitive, chlorotic fleck reactions when challenged with avirulent isolates of P. polysora (1). Rpp resistance prevents or limits the formation of uredinia. The Rpp9 gene has been used successfully in North America in the past 20 years to control southern rust even though the gene has been ineffective in other parts of the world (e.g., Africa and Hawaii) because of the prevalence of virulent races. During the past 3 years, Rpp9 virulence has occurred in the western hemisphere (e.g., Brazil, Mexico, Nebraska, and Texas), but prior to 2008, uredinia were not observed east of the Mississippi River on corn with the Rpp9 gene. A few uredinia were observed on corn with the Rpp9 gene in eastern Nebraska in 2006 and near Victoria, TX in 2007 (W. Dolezal, personal observation). In July of 2008, a virulent isolate of P. polysora was confirmed from Grady County, GA on corn lines with the Rpp9 gene including the original source of this resistance gene, Boesman yellow flint, which is PI 186208 (3). In August of 2008, isolates of P. polysora were collected from severely infected corn hybrids with Rpp9 grown in Macon County, GA. Rust samples from hybrids without Rpp genes also were collected in Burke County, GA where Rpp-resistant corn was asymptomatic. In greenhouse trials, corn lines with and without the Rpp9 gene were inoculated with urediniospores from collections from Burke and Macon counties and Illinois. Rust infection types (1) were scored 18 to 25 days after inoculation. The Macon County isolate produced type 1 and 2 infections (small uredinia surrounded by necrotic or chlorotic tissue) on Oh43Rpp9 and W64aRpp9 and type 4 infections (large, sporulating uredinia) on two versions of a commercial hybrid with and without the Rpp9 gene and on Va59 (which carries an Rpp gene different from Rpp9). The Burke County isolate and an isolate from Illinois collected in 2001 produced type 0 infections (chlorotic flecks) on all of these lines except the non-Rpp version of the commercial hybrid which had a type 4 reaction. To our knowledge, Rpp9-virulent isolates of P. polysora have not been reported from the continental United States for nearly 50 years. In the late 1950s and early 1960s, A. L. Robert (2) collected isolates of P. polysora from throughout the world and observed multiple races on a set of host differentials that is no longer available. A. L. Robert's collection included an isolate from Georgia that was virulent on PI 186208. Commercial hybrids containing the Rpp9 gene may continue to be resistant throughout most of North America if previously common Rpp9-avirulent isolates of P. polysora are prevalent, but those hybrids should be carefully monitored for infection by newly introduced Rpp9-virulent isolates.

Desempenho agronômico de novos híbridos de milho-pipoca no Noroeste do Estado do Paraná

In maize, variations on agronomic performance in distinct environments are common and more evident for one-way hybrids. The objective of this work was to evaluate the performance of new one-way popcorn hybrids developed by the Breeding Program of the State University of Maringa, in northwestern Parana. The characteristics evaluated were: grain yield, popping expansion, plant height, ear height and the intensity of Southern rust ( Puccinia polysora ), Northern leaf blight ( Exserohilum turcicum ), and phaeosphaeria leaf spot ( Phaeosphaeria maydis/Pantoea ananas ). The assay was carried out into randomized block design with three replications in Maringa, state of Parana, Brazil, during the 2006/2007 cropping season. The treatments were 27 simple popcorn hybrids obtained from S5 endogamic inbreds and commercial cultivars BRS Angela, IAC 112 and Jade. Significant differences (p ≤ 0.05) were verified among hybrids for all characteristics. The hybrid from C and K inbreds presented better indexes for grain yield and popping expansion; and was susceptible to Southern rust. About diseases, the hybrids from the L, H and K inbreds showed greater resistance levels to Southern rust, and hybrids from G inbred had better Northern leaf blight resistance. Hybrids from L and M inbreds showed better phaeosphaeria leaf spot resistance.

Resistance to Puccinia polysora in Maize Accessions.

A number of potential sources of general and specific resistance to southern corn rust were identified from 1,890 plant introduction accessions that were screened for reactions to Puccinia polysora race 9. Resistance appeared to differ among four accessions on which uredinia were not observed in initial screenings. Resistance to P. polysora in PI 186215 (Argentine inbred 2-687) was a chlorotic fleck, hypersensitive reaction that was conditioned by a single, dominant gene that was allelic with or very closely linked to the Rpp9 gene based on tests of allelism. All but 3 of 2,357 testcross progeny, (inbred 2-687 × Rpp9) × PS were resistant. Resistance in Ames 19016 (Va59) was effective in F1 progeny and appeared to be dominant and simply inherited; however, this resistance appeared to be a slow-rusting or incomplete resistance that was effective in adult plants but not in young seedlings. Severity of southern rust was less than 10% on resistant progeny from crosses with Va59 compared with severity exceeding 70% on susceptible progeny. Resistance in plant introduction (PI) 186209 (Venezuelan flint) and NSL 75976 (IA DS61) were not effective in F1 hybrid combination and, thus, probably have limited value in commercial maize. Resistance in PI 186209 may be conditioned by a single recessive gene and resistance in NSL 75976 may be co-dominant.

Mapping resistance to Southern rust in a tropical by temperate maize recombinant inbred topcross population

Southern rust, caused by Puccinia polysora Underw, is a foliar disease that can severely reduce grain yield in maize (Zea mays L.). Major resistance genes exist, but their effectiveness can be limited in areas where P. polysora is multi-racial. General resistance could be achieved by combining quantitative and race-specific resistances. This would be desirable if the resistance alleles maintained resistance across environments while not increasing plant maturity. Recombinant inbred (RI) lines were derived from a cross between NC300, a temperate-adapted all-tropical line, and B104, an Iowa Stiff Stalk Synthetic line. The RI lines were topcrossed to the tester FR615 x FR697. The 143 topcrosses were scored for Southern rust in four environments. Time to flowering was measured in two environments. The RI lines were genotyped at 113 simple sequence repeat markers and quantitative trait loci (QTL) were mapped for both traits. The entry mean heritability estimate for Southern rust resistance was 0.93. A multiple interval mapping model, including four QTL, accounted for 88% of the variation among average disease ratings. A major QTL located on the short arm of chromosome 10, explained 83% of the phenotypic variation, with the NC300 allele carrying the resistance. Significant (P < 0.001), but relatively minor, topcross-by-environment interaction occurred for Southern rust, and resulted from the interaction of the major QTL with the environment. Maturity and Southern rust rating were slightly correlated, but QTL for the two traits did not co-localize. Resistance was simply inherited in this population and the major QTL is likely a dominant resistant gene that is independent of plant maturity.

Temporal progress of southern rust in maize under different environmental conditions

The progress of the severity of southern rust in maize (Zea mays) caused by Puccinia polysora was quantified in staggered plantings in different geographical areas in Brazil, from October to May, over two years (1995-1996 and 1996-1997). The logistic model, fitted to the data, better described the disease progress curves than the Gompertz model. Four components of the disease progress curves (maximum disease severity; area under the disease progress curve, AUDPC; area under the disease progress curve around the inflection point, AUDPCi; and epidemic rate) were used to compare the epidemics in different areas and at different times of planting. The AUDPC, AUDPCi, and the epidemic rate were analyzed in relation to the weather (temperature, relative humidity, hours of relative humidity &gt;90%, and rainfall) and recorded during the trials. Disease severity reached levels greater than 30% in Piracicaba and Guaíra in the plantings between December and January. Lower values of AUDPC occurred in later plantings at both locations. The epidemic rate was positively correlated (P &lt; 0.05) with the mean daily temperatures and negatively correlated with hours of relative humidity &gt;90%. The AUDPC was not correlated with any weather variable. The AUDPCi was negatively related to both variables connected to humidity, but not to rain. Long periods (mostly &gt;13 h day-1) of relative humidity &gt;90% (that corresponded to leaf wetness) occurred in Castro. Severity of southern rust in maize has always been low in Castro, thus the negative correlations between disease and the two humidity variables.

Variability in isolates of Puccinia polysora in Brazil

The main objective of this work was to evaluate the variability of the southern rust pathogen Puccinia polysora in Brazil, based on its virulence on a set of maize (Zea mays) cultivars. Sixty single pustule isolates, from different areas of occurrence of southern rust, were evaluated for their virulence to 50 maize experimental hybrids. Six cultivars showed a clear distinction between susceptible and resistant reaction, and were used to characterize the variability of the pathogen. Seventeen virulence patterns were identified among the 60 isolates tested. The most frequent virulence patterns identified, were observed in all locations of sampling, which suggests the absence of geographical differentiation among prevalent populations of P. polysora in Brazil.

NE-EDRsu1 and NE-EDRbt1, Disease-resistant Sweet Corn Populations with sugary1 and brittle1 Endosperms

perate and one-half tropical sweet corn, the latter derived from tropical field corns (Brewbaker, 1978). The tropical parents were chosen for their resistance to important diseases (Brewbaker, 1979). These include the seedling, stalk, and kernel rots caused by Fusarium moniliforme Sheld., and maize mosaic virus (MMV) and maize dwarf mosaic virus (MDMV). Tropical lines also incorporate racially nonspecific tolerance of common rust, southern rust, bacterial leaf blight, northern leaf blight, brown spot, and southern leaf blight. Causal agents are Puccinia sorghi Schw., Puccinia polysora Underw., Pseudomonas avenae Mains, Exserohilum turcicum (Pass.) Leonard & Suggs, Physoderma maydis

Widespread Occurrence of Common Rust, Caused by Puccinia sorghi, on Rp-Resistant Sweet Corn in the Midwestern United States.

Single, dominant resistance genes have been used successfully for the past 15 years to control common rust, caused by Puccinia sorghi, on sweet corn in the United States. Most sweet corn hybrids grown in the Midwest for mid- to late-season processing have Rp resistance, which is expressed as hypersensitive reactions resulting in chlorotic or necrotic flecks with little or no formation of urediniospores. Many, but not all, Rp-resistant sweet corn hybrids carry the gene Rp1D. Biotypes of P. sorghi in North America have been avirulent on plants with the Rp1D gene, except for an isolate collected in Kansas in 1990 (1). In a sweet corn nursery in Urbana, IL, in 1997, small uredinia of P. sorghi occurred on 27 of 79 Rp-resistant sweet corn hybrids that also were infected severely with southern rust caused by P. polysora (2). During August and September 1999, small uredinia or fully susceptible reactions to common rust were observed on several Rp-resistant sweet corn hybrids grown in an area bounded by Mendota, IL, Ripon, WI, and Le Sueur, MN. Southern rust also was prevalent and frequently severe in the area. Isolates of P. sorghi from Rp-resistant corn were collected during September 1999 from Mendota, Rock Falls, and Dekalb, IL; Sun Prairie, Madison, and Ripon, WI; and Rochester, Stanton, and Le Sueur, MN. Ten two-leaved seedlings of one susceptible sweet corn hybrid and five Rp-resistant hybrids, including hybrids known to carry the gene Rp1D, were inoculated in greenhouse trials. Each location (collection) was a separate trial. Inocula were prepared from several uredinia of P. sorghi per location. One set of seedlings also was inoculated with P. polysora. Susceptible reactions (uredinia with urediniospores) were observed on all inoculated seedlings. Uredinia and urediniospores of P. sorghi and P. polysora from seedlings inoculated in the greenhouse were compared directly. All isolates of P. sorghi were confirmed based on 6- to 7-day latent periods, formation of uredinia on both leaf surfaces, and urediniospores that were mostly spherical, cinnamon colored, and moderately echinulate. This is the first widespread occurrence in North America of a biotype of P. sorghi that is virulent on Rp-resistant sweet corn.

Inheritance of resistance to southern corn rust in tropical-by-corn-belt maize populations

The inheritance of resistance to southern rust (caused by Puccinia polysora Underw.) was investigated in two F2:3 populations derived from crossing two temperate-adapted, 100% tropical maize (Zea mays L.) inbred lines (1416-1 and 1497-2) to a susceptible Corn Belt Dent hybrid, B73Ht×Mo17Ht. The inbred lines possess high levels of resistance to southern rust and may be unique sources of resistance genes. Heritability for resistance was estimated as 30% and 50% in the two populations from regression of F2:3 family mean scores on F2 parent scores, and as 65% and 75% from variances among F2:3 families on a single-plot basis. RFLP loci on three chromosomal regions previously known to possess genes for resistance to either southern rust or common rust (P. sorghi Schw.) were used to localize genes affecting resistance to southern rust in selected genotypes of both populations, and to estimate their genetic effects. A single locus on 10S, bnl3.04, was associated with 82–83% of the variation among field resistance scores of selected F2:3 families in the two populations. Loci on chromosomes 3 (umc26) and 4 (umc31) were significantly associated with resistance in the 1497-2 population, each accounting for 13–15% of the phenotypic variation for F2:3 field scores. Multiple-marker locus models, including loci from chromosomes 3, 4, and 10 and their epistatic interactions, accounted for 96–99% of the variation in F2:3 field scores. Similar results were obtained for resistance measured by counting pustules on juvenile plants in the greenhouse. An attempt was made to determine if the major gene for resistance from 1416-1 was allelic to Rpp9, which is also located on 10S. Testcross families from the cross (1416-1×B37Rpp9)×B14AHt were evaluated for resistance to southern rust in Mexico. Neither source of resistance was completely effective in this environment, preventing determination of allelism of the two genes; however, both sources of resistance had better partial resistance to southern rust than did B14AHt.

トウモロコシ南方さび病の発生消長

トウモロコシ南方さび病の発生消長