Jerry W. Johnson

A molecular marker associated with the H21 Hessian fly resistance gene in wheat

Near-isogenic lines in conjunction with bulked segregant analysis were used to identify a DNA marker in wheat (Triticum aestivum L.) associated with the H21 gene conferring resistance to biotype L of Hessian fly [Mayetiola destructor (Say)] larvae. Near-isogenic lines were developed by backcross introgression BC3F3:4 (‘Coker 797’ * 4 / ‘Hamlet’) and differed by the presence or absence of H21 (on 2RL) derived from ‘Chaupon’ rye (Secale cereale L.). Bulked DNA samples were prepared from near-isogenic lines and BC3F2 population individuals segregating for reaction to Hessian fly biotype L and screened for random amplified polymorphic DNA markers using 46 10mer primers. Random-amplified polymorphic DNA markers from resistant and susceptible individuals and parental lines were scored and these data were used to identify a 3 kb DNA fragment that was related to the occurrence of H21. This fragment was amplified from DNA isolated from Hamlet, a near-isogenic line carrying 2RL, and bulked DNA from resistant BC3F2 individuals, but not from the recurrent parent Coker 797 or DNA bulks from susceptible BC3F2 plants. Analysis of 111 BC3F2 segregating individuals and BC3F2:3 segregants confirmed the co-segregation of the 3 kb DNA marker with the H21 resistance gene to Hessian fly. Use of this marker could facilitate more rapid screening of plant populations for Hessian fly resistance and monitoring the introgression of H21.

Molecular characterization of a new powdery mildew resistance gene Pm54 in soft red winter wheat

Key messageA new powdery mildew resistance genePm54was identified on chromosome 6BL in soft red winter wheat.AbstractPowdery mildew is causing increasing damage to wheat production in the southeastern USA. To combat the disease, a continuing need exists to discover new genes for powdery mildew resistance and to incorporate those genes into breeding programs. Pioneer® variety 26R61 (shortened as 26R61) and AGS 2000 have been used as checks in the Uniform Southern Soft Red Winter Wheat Nursery for a decade, and both have provided good resistance across regions during that time. In the present study, a genetic analysis of mildew resistance was conducted on a RIL population developed from a cross of 26R61 and AGS 2000. Phenotypic evaluation was conducted in the field at Plains, GA, and Raleigh, NC, in 2012 and 2013, a total of four environments. Three quantitative trait loci (QTL) with major effect were consistently detected on wheat chromosomes 2BL, 4A and 6BL. The 2BL QTL contributed by 26R61 was different from Pm6, a widely used gene in the southeastern USA. The other two QTL were identified from AGS 2000. The 6BL QTL was subsequently characterized as a simple Mendelian factor when the population was inoculated with a single Blumeria graminis f. sp. tritici (Bgt) isolate in controlled environments. Since there is no known powdery mildew resistance gene (Pm) on this particular location of common wheat, the gene was designated Pm54. The closely linked marker Xbarc134 was highly polymorphic in a set of mildew differentials, indicating that the marker should be useful for pyramiding Pm54 with other Pm genes by marker-assisted selection.

Nutrient accumulation and distribution of wheat genotypes in response to waterlogging and nutrient supply

The effect of soil waterlogging and nutrient supply on plant nutrient accumulation and distribution was investigated for two genotypes of winter wheat (Triticum aestivum L.) differing in waterlogging resistance, ‘Bayles’ and ‘Savannah’. Plants were grown in waterlogged or drained sand and fertilized with half-strength or full-strength Hoaglands solution.Waterlogging reduced the concentrations of N, P, K, Mg, and Zn in leaves and stems and increased the concentrations of those elements in the root system. The effects were greater for waterlogging-sensitive Bayles than for waterlogging-resistant Savannah. Higher concentrations of Fe and Mn were found in waterlogged plants compared to the control plants for sensitive Bayles. Waterlogging increased the proportion of N and Zn in the root system and decreased that of K in stems for Bayles. The proportion of Fe increased in leaves and stems for Bayles and Savannah under waterlogged conditions, but to a greater extent for Bayles. Doubling the concentrations of all major and minor nutrient elements supplied to the waterlogged rooting medium improved plant nutrient status and enhanced plant dry matter production.

Development of AFLP and STS markers for identifying wheat-rye translocations possessing 2RL

Wheat-rye translocation line (2BS/2RL) has been developed for resistance to biotype L of Hessian fly and agronomically useful traits. AFLP analysis using 64 primer pairs was conducted in order to identify 2RL-specific polymorphisms between “Coker 797” (non-2RL), near-isogenic line (NIL) carrying 2RL, and “Hamlet”. Nine primer combinations identified twelve reproducible polymorphic fragments in the NIL carrying 2RL. These twelve fragments were cloned and sequenced with an aim towards converting AFLP markers into sequence tagged sites (STS). A comparison of the 12 sequences with non-redundant accessions in the NCBI database using the BLAST search option indicated that one fragment of approximately 200 bp in length (amplified using primer combination E+AAC / M+CTA) was highly homologous with the rye-specific repetitive sequence R173-1 and Wis-2-lA, a retrotransposon-like element in wheat. Two STS primers (SJ07 and SJ09) out of twelve STS primer sets enabled the detection of polymorphisms between Coker 797 and NIL carrying 2RL. In order to verify whether the polymorphism detected by primers SJ07 and SJ09 was in fact the result of the presence of 2RL, additional plant material was examined. Amplified products of about 260 bp fragment with the SJ07 primer set were generated in rye cvs.“Chilbohomil” and “Jochunhomil”, triticale experimental line Suwon 15, and wheat experimental line K-14 (1AL/1RS & 2BS/2RL), as well as NIL carrying 2RL and Hamlet, but not in Coker 797 (non-2RL), “Keumgangmil” (non-translocation wheat), KS92WGRC17 (PI592729 /;/ 6BS/6BL-6RL), KS92WGRC19 (P1592731 /;/ 4BS/4BL-6RL), “TAM200” (1AL/1RS), and “Siouxland” (1BL/1RS). Our data suggest that primer set SJ07 amplifies a “2RL-specific” fragment of diagnostic value.

Responses of squash to salinity, waterlogging, and subsequent drainage: I. Gas exchange, water relations, and nitrogen status

Abstract To examine plant physiological responses to salinity, waterlogging, and subsequent drainage, summer squash (Cucurbita pepo) was grown in well watered or flooded sand with full‐strength Hoagland solution containing 100 mol/m3 sodium chloride (NaCl) or no NaCl for 14 d. Half of the waterlogged plants were transferred to drained conditions for 7 d of recovery, while half of salinized plants were continuously salinized until 21 d. Waterlogging or salinity alone reduced photosynthetic rate (Pn), stomatal conductance (gs), and leaf chlorophyll content to a greater extent with waterlogging. Waterlogging alone, however, did not affect leaf water potential (ψ leaf) Salinity alone did not affect leaf and root nitrogen content. A combination of waterlogging and salinity exacerbated the adverse effects of each factor alone for Pn, gs, leaf chlorophyll, and nitrogen content, but not for ψ leaf. Seven days after termination of waterlogging, a full recovery occurred for gs, ψ leaf, leaf chlorophyll content, and...

Components of partial resistance to Leptosphaeria nodorum among seven soft red winter wheats

SummarySeven soft red winter wheat cultivars were evaluated for partial resistance to Leptosphaeria nodorum under field conditions. The results demonstrate that resistance is available among cultivars that are adapted to the southeastern U.S. and that resistance is long lasting. Resistant cultivars had longer incubation and latent periods, slower rates of lesion development, and reduced the level of sporulation of L. nodorum. Seedlings of susceptible cultivars sustained severe disease with dew periods as short as 48 hr in greenhouse tests. One resistant cultivar sustained little damage with dew period as long as 144 hr.Latent period was shortest on the second leaf below the flag leaf (F-2 leaf) of all cultivars and longest on the flag leaf which reflected the effect of microclimate and leaf age. The range in length of latent period on the flag, F-1, and F-2 leaves of resistant cultivars was less than that for susceptible cultivars. Differences between cultivars were greatest (up to 6.8 days) for the F-2 leaf. A delay in production of inoculum on the F-2 and lower leaves of resistant cultivars should delay infection of the flag leaf and spike.The greatest differentiation among cultivars for sporulation of L. nodorum was on upper leaves at Feekes growth stage 11.2. ‘Oasis’ consistently had less sporulation than other cultivars at all sampling dates and leaf positions. The rate of disease progress up the plant (disease severity) and area under the disease progress curve were also least on ‘Oasis’.There were significant correlations among components of resistance and associated components suggesting that a single or interrelated mechanisms control expression of resistance. Overall, ‘Oasis’ was the most resistant cultivar followed by ‘Coker 762’ and ‘Coker 747’. There cultivars have remained resistant for ten or more years. ‘Stacy’ was intermediate in resistance and was the most variable of the seven cultivars for the components tested. ‘Holley’, ‘Omega 78’, and ‘Florida 301’ were highly susceptible by all criteria tested. Plant height was not a factor in resistance. The resistant cultivars are mostly later in maturity than the susceptible cultivars. In this study, crop maturity was similar under existing environmental conditions during the two seasons when most data were collected.

Wheat growth responses of cultivars to H+ concentration

Shoot length (cm), shoot fresh weight (g/pot), root length (cm), and root fresh weight (g/pot) were measured on six cultivars of wheat (Triticum aestivum L. cv Saluda, C9733, Gore, Stacy, FL301, and FL302) grown at pH 6.0, 5.5, 5.0, 4.5, or 4.0 for 14 days in ‘white quartz flintshot’ sand. Plants were watered on alternate days with pH-adjusted buffer solutions. All measured plant parameters decreased as H+ concentration increased from pH 6.0 to 4.0. Decreased lengths of shoots and roots were similar among the cultivars as the pH decreased. This indicated a uniform response of wheat cultivars to excess H+ concentration in the soil solution; however, the decrease in shoot and root length was only about 50% as large as was previously reported for sorghum [Sorghum bicolor (L.) Moench.].

Environmental stability and heritability estimates for grain yield and test weight in triticale

Hexaploid triticale has many advantages over both parental species for both grain and forage production in certain environments. Additional information on environmental stability and heritability would be desirable to develop appropriate selection strategies in the production of superior widely-adapted cultivars. The grain yield of 22 diverse genotypes grown at four ecologically-distinct geographical locations [Quincy, FL, USA (approximate geographical coordinates (AGC) = 30°N 84°W, approximate elevation (AE) = 58 m), Plains, GA, USA (AGC = 32°N 84°W, AE = 76 m), Bozeman, MT USA (AGC = 45°N 111°W, AE = 1458 m), and Aberdeen, ID, USA (AGC = 42°N 112°W, AE = 1360 m)] was measured in two years with winter and spring planting dates only at Bozeman and Aberdeen. Test weight (grain weight in a given volume) was determined for two years at Bozeman and Aberdeen at both planting dates and one year at Quincy. Stability analyses indicated that significant (P < 0.01) variation in means, regression coefficients, and deviation mean squares of the genotypes were present for both characters. Realized heritability (h2) estimates were as follows: grain yield ranged from −0.02 to 0.80 with a mean of 0.57; test weight ranged from 0.63 to 1.05 with a mean of 0.93. The results indicated that substantial genetic variation is present and selection for widely-adapted cultivars would be effective for both characters especially test weight.

Responses of squash to salinity, waterlogging, and subsequent drainage: II. Root and shoot growth

Abstract The responses of root and shoot growth to concurrent salinity and waterlogging, and subsequent drainage of summer squash (Cucurbita pepo) were studied in a greenhouse experiment. Plants were well watered or flooded with full‐strength Hoagland solution containing 100 mol/m3 sodium chloride (NaCl) or no NaCl for 14 d. Waterlogged plants were then transferred to drained conditions for 7 d of recovery, while salinized plants were continuously salinized until 21 d. Waterlogging led to greater reductions in root and shoot growth, and fruit yield than did salinity. Waterlogging stimulated production of adventitious roots; however, salinity suppressed this enhancement effect. A combination of waterlogging and salinity exacerbated the adverse effects of each factor alone on root and shoot growth. Seven days after termination of waterlogging, a full recovery occurred for number and length of adventitious roots, number of lateral roots, and root dry weight for waterlogged plants under non‐saline conditions,...

Relationship of glume blotch symptoms on wheat heads to seed infection by Septoria nodorum.

Glume blotch on wheat heads was assessed visually in field plots. There was no correlation between head symptoms and seed infection caused by Septoria nodorum . Secondly, individual seeds were assigned to several severity classes based on the area of their lemmas that exhibited glume blotch symptoms. Seed infection was related to lemma symptoms only when the area exhibiting symptoms was > 0% and S. nodorum was more superficial than colonization associated with greater lemma symptom severities. High possession (i.e. extensive colonization) of infected seeds was directly related to the severity of lemma symptoms. The extent to which S. nodorum colonizes wheat seeds may be more important than the percentage of infected seeds. Thousand kernel weight was inversely related to the severity of lemma symptoms; maximum kernel weight reduction was reached when the area of blotching exceeded 50%.