Constitution of resistance to common cutworm in terms of antibiosis and antixenosis in soybean RIL populations

Common cutworm (CCW; Spodoptera litura Fabricius) is a major leaf-feeding pest in Asia. The focus of this study was to explore the genetic mechanism for resistance to CCW in terms of antibiosis and antixenosis through mapping QTL (Quantitative trait locus/loci) in soybean using two recombinant inbred line populations. Larva weight (LW) and pupa weight (PW) were evaluated as indicators for antibiosis and damaged leaf percentage as the indicator for antixenosis to CCW. The obvious transgressive segregation indicated a complementary genetic status between the parents. The genetic structure for antibiosis and antixenosis was similar, about 51.1–75.7 % of the phenotypic variation (PV) accounted for by genetic variation, where 42.2–60.3 %, or the majority, was explained by the collective unmapped minor QTL. And, 0–6 additive QTL each explained 0.0–11.8 % in a total of 0.0–27.4 % of PV, and 0–3 epistatic QTL pairs each explained 0.0–7.6 % in a total of 0.0–14.0 % of PV. However, the detected QTL compositions for antibiosis and antixenosis were quite different with only one QTL qCCW10_1 shared by both antibiosis and antixenosis with 8.9–11.8 and 4.7 % contribution to PV, respectively. Within antibiosis between LW and PW, the detected QTL overlapped (r = 0.53–0.78). Among the detected QTL, qCCW6_1, qCCW10_1 and qCCW12_2 were the major contributors to antibiosis, and qCCW10_1, qCCW10_2 and qCCW12_1 the major contributors to antixenosis. Since only some major QTL could be used for marker-assisted breeding, the main concern is how to use the large amount of undetected minor QTL.     

Glutenin allelic variation and 1AL.1RS effects on dough mixing properties of wheat grown in irrigated and rainfed environments

Wheat (Triticum aestivum L.) glutenin allelic variation and presence of the 1AL.1RS wheat-rye (Secale cereale L.) translocation play important roles in determining end-use quality. This study was conducted to evaluate the effects of high and low molecular weight glutenin alleles and 1AL.1RS on dough mixing properties of 189 recombinant inbred lines (RILs) from the cross TAM 107-R7/‘Arlin’ grown in irrigated and rainfed Colorado (USA) environments. The results indicated that (1) higher values (P < 0.05) of some dough mixing properties were observed for Glu-A1b versus Glu-A1a, Glu-B1b versus Glu-B1c, Glu-D1d versus Glu-D1a, and non-1AL.1RS versus 1AL.1RS; (2) no differences in Mixograph properties were found for Glu-A3c versus Glu-A3e, Glu-B3e versus Glu-B3g, or Glu-D3a versus Glu-D3b; (3) although variation at some glutenin loci had little effect on Mixograph properties, pairwise combinations of glutenin loci or a glutenin locus combined with 1AL.1RS affected most Mixograph traits; and (4) in general, the effects of glutenin alleles and 1AL.1RS on dough mixing properties did not differ greatly between the irrigated and the rainfed environment. These results will be useful for assessing potential wheat quality and directing wheat breeding efforts in Colorado and similar environments.     

Genome re-arrangements associated with loss of pathogenicity of the gamma-herpesvirus alcelaphine herpesvirus-1

The alcelaphine herpesvirus 1 (AlHV-1) causes malignant catarrhal fever in ruminants. Previous work had shown that serial passage of AlHV-1 in culture resulted in genome alterations that are associated with a loss in pathogenicity. Here we have analysed the re-arrangements that occur in more detail. None of the observed re-arrangements was entirely consistent. However, they did all involve translocation of a similar region of DNA from around the centre of the genome to areas either next to or in between terminal repeat elements at either end of the genome. There was also a concomitant loss of the wild-type locus. These re-arrangements appeared to be associated with the loss of virulence and the appearance of cell-free virus.     

Dehydrodimers of Ferulic Acid in Maize Grain Pericarp and Aleurone: Resistance Factors to Fusarium graminearum

ABSTRACT The relationship between the primary cell wall phenolic acids, dehydrodimers of ferulic acid, and maize grain resistance to Fusarium graminearum, the causal agent of gibberella ear rot, was investigated. Concentrations of dehydrodimers of ferulic acid were determined in the pericarp and aleurone tissues of five inbreds and two hybrids of varying susceptibility and in a segregating population from a cross between a resistant and susceptible inbred. Significant negative correlations were found between disease severity and diferulic acid content. Even stronger correlations were observed between diferulic acid and the fungal steroid ergosterol, which is an indicator of fungal biomass in infected plant tissue. These results were consistent over two consecutive field seasons, which differed significantly for temperature and rainfall during pollination, the most susceptible stage of ear development. No correlation was found between the levels of these phenolics and deoxynivalenol levels. This is the first report of in vivo evidence that the dehydrodimers of ferulic acid content in pericarp and aleurone tissues may play a role in genotypic resistance of maize to gibberella ear rot.     

A mathematical simulation of growth of fusarium in maize ears after artificial inoculation

ABSTRACT Fusarium spp. in maize can contaminate the grain with mycotoxins if environmental conditions are favorable for fungal growth. To quantify the relationship between growth of Fusarium spp. and environmental conditions, a mathematical model was developed to simulate growth of F. graminearum and F. verticillioides on maize ears following silk inoculation in field experiments from 1992 to 1995. Each species was inoculated separately and as a mixture of the two for 3 of the 4 years on one maize hybrid. Disease progress in ears was measured by a visual rating scale that was converted to percent visual infection. Measurements were made at regular time intervals after silks were inoculated 5 days after silk emergence. Differential equations were used to relate growth rates of Fusarium spp. in maize ears to hourly air temperature and relative humidity and to daily precipitation. Integration of these equations over time produced quantitative estimates of fungal growth. Model calculations compared well with measurements (R(2) = 0.931, standard error of estimate [SEE] = 2.11%) of percent visual disease infection of maize ears over 3 years. The model was tested against a second set of data (R(2) = 0.89, SEE = 5.9%) in which silks were inoculated at nine different times after first silk emergence for each of 2 years (1994 and 1995) with the two species of fungi on the same maize hybrid. At this time, a silk function was developed to account for changes in the susceptibility of silks to disease. F. graminearum responded to wet conditions more than F. verticillioides, and for the conditions of this experiment, grew much faster than F. verticillioides when inoculated separately. When they were inoculated together, F. graminearum growth rates were much lower, indicating some interference by F. verticillioides. During 1993, weather conditions before inoculation reduced the growth of both species in silks.     

Polymerase Chain Reaction Assays for the Detection and Discrimination of the Soybean Rust Pathogens Phakopsora pachyrhizi and P. meibomiae

ABSTRACT Soybean rust occurs in Australia and many countries throughout Africa, Asia, and South America. The causal agents of soybean rust are two closely related fungi, Phakopsora pachyrhizi and P. meibomiae, which are differentiated based upon morphological characteristics of the telia. Determination of the nucleotide sequence of the internal transcribed spacer (ITS) region revealed greater than 99% nucleotide sequence similarity among isolates of either P. pachyrhizi or P. meibomiae, but only 80% sequence similarity between the two species. Utilizing differences within the ITS region, four sets of polymerase chain reaction (PCR) primers were designed specifically for P. pachyrhizi and two sets for P. meibomiae. Classical and real-time fluorescent PCR assays were developed to identify and differentiate between P. pachyrhizi and P. meibomiae. Identification of P. pachyrhizi from infected soybean leaves using the real-time PCR assay will allow for more rapid diagnoses.