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a USDA-ARS, Crop Production and Pest Control Research Unit, W. Lafayette, IN 47907
b Dep. of Agronomy, Purdue Univ., W. Lafayette, IN 47907
* Corresponding author (roger_ratcliffe{at}entm.purdue.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Abbreviations: CI, a number assigned by the former Division of Cereal Crops and Diseases • GRIN, Germplasm Resources Information Network • PI, plant identification number of the USDA-ARS National Small Grains Collection, Aberdeen, ID
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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During the 1990s, 87 Hessian fly populations from the eastern USA soft winter wheat region were evaluated for biotype composition (Ratcliffe et al., 1994, 1996, 2000, unpublished data, 2000). These populations were broadly grouped into five areas; northeast (New York and Pennsylvania), mid-Atlantic (Delaware, Maryland, North Carolina, and Virginia), southeast (Florida, Georgia, and South Carolina), mid-south (Alabama, Arkansas, Louisiana, Mississippi, and Tennessee), and Midwest (Illinois, Indiana, Michigan, Missouri, and Ohio). In addition to testing field populations for biotype composition, selected populations were increased and maintained for testing against wheat germplasms and cultivars being developed in the Purdue soft winter wheat breeding program (Ratcliffe, 2000). Hessian fly populations selected for further testing were considered representative of those collected within specific regions of the eastern USA.
Previous tests of wheat germplasms with Hessian fly resistance included lines in both common (soft and hard winter wheat) and durum backgrounds and with deployed and undeployed resistance genes (Ratcliffe et al., 1994, 1996, 2000). Hessian fly populations from the southeastern USA demonstrated the greatest range in virulence to both deployed and undeployed resistance genes and populations from the mid-Atlantic area demonstrated the highest frequency of virulence to undeployed genes, particularly H13. In contrast, fly populations from the mid-south and Midwest were relatively uniform in biotype composition (primarily biotype L) and demonstrated less virulence to undeployed genes. Hessian fly incidence in northeastern states was very low during the 1990s and consequently insufficient data were collected during this time on biotype composition to be of value. Because of limited seed supply of many of the wheat lines reported herein, tests were conducted on only four Hessian fly populations collected in 1999 from the mid-Atlantic and southeastern states. These were considered representative of eastern USA populations demonstrating greatest diversity in virulence to resistance genes, as described above.
The rationale for determining gene number conditioning resistance to Hessian fly biotypes D or L in relation to resistance to eastern USA populations is that the same genes may be effective for both. This relationship appears most clear where there is only one gene for resistance to biotype D or L and where resistance to one or more eastern USA populations occurs. Where two or more genes condition resistance to biotype D or L, then at least one may provide resistance to the eastern USA populations. Hessian fly biotype D is virulent on wheat genotypes with deployed resistance genes H3, H6, or H7H8, but not on those with gene H5. Biotype L is virulent on wheat genotypes with any of the above deployed genes. Neither biotype D or L is virulent on wheat genotypes with recently deployed H13.
The objectives of this research were to (i) use 26 durum wheat genotype reactions to evaluate similarities and differences in virulence among four eastern USA Hessian fly populations, (ii) determine which durum germplasm lines offered the best potential usefulness as sources of resistance to the four Hessian fly populations, and (iii) determine the number of genes conditioning resistance to laboratory biotype L of Hessian fly in 11 durum wheat PI lines for which gene number was not known.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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12 cm from top of plants to cheesecloth) when plants were in the two-leaf stage and were infested with 300 gravid females for 3 to 4 d, after which the tent was removed. To eliminate cross contamination of populations, plants in flats infested with each population were isolated until adults were dead. Flats were held in growth chambers at 18°C and a photoperiod of 12:12 (L:D) h throughout the test. Illumination within chambers was approx. 650 to 700 µmol m-2 s-1. Plant response to larval infestation was recorded after 19 to 21 d. All plants were removed from the flat, rated as susceptible or resistant, and dissected to determine the presence or absence of larvae, larval survival and approximate stage of development of living larvae. Data were recorded as the number of resistant and susceptible plants for each entry and converted to percentage resistant or susceptible plants per entry. The relative resistance or susceptibility of wheat lines/cultivars was expressed as resistant (90–100% resistant plants), moderately resistant (76–89% resistant plants), or susceptible (0–75% resistant plants). A Hessian fly population was expressed as virulent to a wheat selection when 25% of the plants within the selection were susceptible to the fly population.
Sources of Resistant Germplasm
Most of the durum lines resistant to Hessian fly biotypes D and L were identified in tests by personnel of the USDA-ARS, Crop Production and Pest Control Research Unit at Purdue University in cooperation with the USDA-ARS National Small Grains and Potato Germplasm Research Unit, Aberdeen, ID. The country of origin and other information on this group of germplasm lines was provided from records of the USDA-ARS, National Germplasm Resources Laboratory, Beltsville, MD (Table 2).
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Seven CI Lines
Five lines, CI 3146 to CI 7535 (Table 3) previously were evaluated for number of genes for resistance to Hessian fly biotypes D or L at 19 or 21°C, for resistance interrelationships, and for their differences from known resistant tester stocks with genes H5, H9, H14, or H16 (Cambron et al., 1995). Germplasm line CI 7539 previously was tested to biotype L in backcross populations; germplasm line CI 15160 was derived from a progeny of CI 15160 that had better resistance to biotype L at 25°C. Resistance was conditioned by one gene in CI 3146 (Cambron et al., 1995) and CI 3984 (Ohm, Patterson, unpublished data, 1995), two genes in CI 7041 and CI 7066 (Cambron et al., 1995) and CI 7539 (Ohm, Patterson, unpublished data, 1995), and three genes in CI 7535 (Cambron et al., 1995) and CI 15160 (Ohm, Patterson, unpublished data, 1995). The single genes conditioning resistance to Hessian fly biotype L in CI 3146 and in CI 3984 appear to be alleles based on results of testcross F2 family analysis (Ohm, Patterson, unpublished data, 1995) and different reactions to Hessian fly populations in this study and in a field test at Griffin, GA (J.J. Johnson, personal communication, 2000).
Five Additional Lines
Five lines were selected from germplasm demonstrating resistance in tests conducted at Manhattan, KS (Jori), and West Lafayette, IN (Giorgio 331, PI 428435, P80164H5, and P84702H12). Resistance was conditioned by one gene in each of the five lines as follows; Jori (Amri et al., 1990), PI 428435 (Obanni et al., 1988), P80164H5 and P84702H12 (Patterson et al., 1994), and Giorgio 331 (Ohm, Patterson, unpublished data, 1995). P80164H5 (H16) and P84702H12 (H19) each resulted from one backcross of the resistance gene donor line to susceptible durum line D6647 (Lebsock et al., 1972).
Lines with Unknown Gene Number
Eleven durum germplasm lines, PI 134942 to PI 323440 (Table 3), were selected for study from a group of 50 resistant lines based on resistance to biotype L at 25°C (Unpublished data, 1995). The 50 resistant lines were identified among a group of lines from the USDA-ARS National Small Grains Collection by USDA-ARS and Purdue University personnel as part of the Germplasm Resources Information Network (GRIN) initiative.
Common Wheat Selections
Common wheat selections compared with durum lines were germplasm lines P921682A4, Lola, and the cv. INW9811. P921682A4 (H16) was selected following six backcrosses of P80164H5 (H16) durum germplasm line to ‘Newton’ (CI 17715) common wheat (Patterson et al., 1988). Lola (H12) was selected from the backcross Newton*4/'Luso' (Patterson et al., 1994). Luso common wheat was shown to have one gene which conditioned resistance to biotypes B and D at 20°C (Oellermann et al., 1983). Resistance gene H12 has not been deployed for resistance to Hessian fly in cultivars in the USA. INW9811 (H13) is a soft red winter wheat cultivar released by Purdue University and the USDA-ARS in 1998 for production in the eastern USA (Ratcliffe et al., 2000). Resistance was derived from Triticum tauschii (Coss) Schmal. (Martin et al., 1982). H13 was mapped on chromosome 6D of wheat (Gill et al., 1987). The H13 gene conditions excellent resistance to Hessian fly biotypes D and L at temperatures of 19 to 25°C. Lola and INW9811 previously were evaluated for resistance to Hessian fly populations collected from the mid-Atlantic and southeastern USA in the late 1980s and mid-nineties, respectively (Ratcliffe et al., 1994, 2000). The four differential cultivars used in defining Hessian fly biotypes were Monon, Magnum, Caldwell, and Seneca. These cultivars have been deployed in the eastern USA and these genes for resistance have been deployed in other cultivars as well, beginning with Seneca (CI 12529, H7H8) in 1949, ‘Dual’ (CI 13083, H3) in 1955, ‘Knox 62’ (CI 13701, H6) in 1962, and ‘Arthur 71’ (CI 15282, H3H5) in 1971.
Estimating Number of Genes Conditioning Resistance
The Chi-square goodness-of-fit test with adjustment for small numbers (Steel and Torrie, 1980) was used to estimate the number of genes conditioning resistance to Hessian fly biotypes D and L. Analyses were based on reactions of F2 families from backcross or testcross tests. In most cases 80 or 90 families, parents, and check plants were grown in 10 greenhouse flats and infested with Hessian fly and placed in a growth chamber for 19 to 21 d before determining plant reactions. A family was represented by about 25 or 30 plants. Pure biotypes D or L were used. Biotype L is the more virulent biotype. In tests of a germplasm line, materials were derived from the progeny of a single typical selfed plant then tested for resistance to Hessian fly. In classifying backcross or testcross F2 families, the distinction was between those families segregating for resistant and susceptible plants and those families where all plants were susceptible.
Resistant Reactions of Heterozygous Plants
Resistance of wheat to Hessian fly is expressed most often as partial dominance. The method suggested by Obanni et al. (1988) was used to estimate the expression of resistance of plants heterozygous for a single gene for resistance. In those backcross families segregating for a single factor, a 1:2:1 ratio of homozygous resistant (RR) to heterozygous (Rr) to susceptible (rr), F2 plants is expected. The homozygous resistant F2 plants should express resistance similar to plants of the resistant parent. The number of resistant and the number of susceptible F2 plants within segregating families were summed. An example is presented to illustrate the method. With 400 F2 plants total, 100 would be expected to be RR, 200 to be Rr, and 100 rr. If the total number of resistant F2 plants was 200 then 200 minus 100 RR plants leaves 100 Rr, i.e., 50% of the heterozygous plants expressed resistance.
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RESULTS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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There was 100% mortality of larvae observed on resistant plants of 18 of the 26 durum lines. This included Port 2536, Port 2852, Rebeiro, CI 3984, CI 7041, CI 7066, CI 7535, CI 15160, PI 134942, PI 166947, PI 185410, PI 185721, PI 192839, PI 192840, PI 192851, PI 323440, Jori, and P80164H5. There were living and dead larvae on some plants of CI 3146 and PI 192738 although all plants were classified as resistant. Living larvae on resistant plants of both durum and common wheat selections ranged in size, but generally were smaller (estimated to be mostly late first to early second instar) than larvae on susceptible plants of the same wheat selection. Larvae had developed to the flaxseed stage (late second to third instar) on most susceptible plants, but there were no flaxseed observed on resistant plants of any wheat selection.
Number of Genes Conditioning Resistance in 11 PI Lines
Data are summarized in Table 4. Check plants of the recurrent backcross parent D6647 were all susceptible, plants of the nonrecurrent parents were nearly all resistant, and plants of the Molly (H13) check (not shown) were all resistant. There was good precision in the 11 backcross analyses of the number of genes conditioning resistance in these durum germplasm lines.
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The resistance of PI 185721 segregated in a backcross ratio indicating that a single dominant or partially dominant gene conditioned the resistance to biotype L. All plants of the resistant parent were resistant (Table 4). From a total of 782 F2 plants in segregating families, 462 plants were resistant. After subtracting 195 calculated homozygous types, 267 or about 68% of the plants heterozygous for resistance expressed resistance. The backcross analysis of the resistance of PI 192351 indicated that resistance was conditioned by two dominant or partially dominant genes. All plants of PI 192351 were resistant. The resistance of PI 192738 in the backcross segregated in a good fit to a 1:1 ratio indicating a single dominant or partially dominant gene conditioned the resistance of PI 192738 (Table 4). Of a total of 984 F2 plants within segregating families, 364 plants tested resistant. Of those, 118 or about 24% were calculated as heterozygous for resistance. All parent plants were resistant.
The backcross F2 family analysis for PI 192839 indicated that resistance was conditioned by two dominant or partially dominant genes. All plants of PI 192839 were resistant (Table 4). PI 192840 appeared to have three genes segregating for resistance to biotype L. All plants of the resistant parent were resistant (Table 4). This parent and PI 192839 are recorded as having the same name (Table 2), but the difference in gene number for resistance is distinct in these analyses.
The resistance of PI 192851 appears to be conditioned by one dominant or partially dominant gene from the segregation of backcross families (Table 4). More than 99% of the parent plants were resistant. Of a total of 1050 F2 plants within segregating families, 676 were resistant, with 414 or about 79% of the heterozygous plants calculated to express resistance.
Estimating the number of genes for resistance of PI 274681 was more puzzling. About 95% of the parent plants were resistant. The segregation of backcross F2 families gave a poor fit to a 1:1 ratio and an unacceptable fit to a 3:1 ratio (Table 4). This may result from linkage of two genes calculated at about a 24-centimorgan separation.
The resistance of PI 323440 appeared to be conditioned by a single dominant or partially dominant factor. All plants of PI 323440 were resistant (Table 4). Plants of PI 323440 and resistant F2 plants exhibited the stunting and growing out reactions described above for PI 185410. The two lines have different recorded areas of origin (Table 2). There were 928 F2 plants in the segregating backcross families of which 522 were resistant. This leaves a calculated 290 or about 65% of the heterozygous F2 plants that expressed resistance.
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DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The susceptibility of PI 428435 (H17) was unexpected because resistance (95–100%) to fly populations from Maryland was observed in previous tests with H17 in the same durum line (Ratcliffe et al., 1994). However, tests reported by Ratcliffe et al. (1994) were conducted with fly populations collected in Maryland in 1989. Changes within Maryland populations for the relative frequency of virulence genes occurred during this time. The two populations tested by Ratcliffe et al. (1994) and the population tested by us (Table 1) were collected from the same general area of the Eastern Shore of Maryland; however, the frequency of biotype L was much higher in the 1999 (96%) than the 1989 populations (35 and 54%). Ratcliffe et al. (1994) reported that virulence to gene H9, which confers resistance to biotype L, differed among fly populations that were classified as predominately biotype L but were collected from different geographical locations in the eastern USA. As noted by Ratcliffe et al. (1994), biotype L, as identified in tests reported here, is defined by the ability to infest all of the four differential hosts with the wheat genes H7H8, H3, H5, and H6. However, biotype L may be represented not by a single virulence gene but by several different virulence genes (Ratcliffe et al., 1994). Similarly, although H17 is resistant to biotype L, it is possible that virulence to H17 within populations composed largely of biotype L may differ and that the reduced effectiveness of H17 that we observed may be related to the increase in frequency of biotype L in fly populations from this area of Maryland. This possibility illustrates the importance of evaluating new resistance genes for response to current geographical populations of the Hessian fly, as well as laboratory biotypes, when making decisions on genes to incorporate into common wheat cultivars.
Caldwell et al. (1946) observed the presence of low numbers of living larvae on plants carrying resistance from ‘Illinois No. 1’W38 (H3) but these plants demonstrated no symptoms of infestation (phenotypically resistant). They reported that a large proportion of the puparia on these resistant plants were abnormally small or contained dead larvae. These authors also observed the capacity of some plants that contained larvae to recover from slight stunting; this response was seen particularly when tests were conducted in the field or greenhouse at temperatures above 20°C. Caldwell et al. (1946) described resistance in this material both as the plants' capability to prevent larval development under conditions favorable for the expression of resistance as well as to grow normally, although infested, under less favorable conditions. In both cases, plants expressed effective levels of resistance to Hessian fly. Recovery after stunting was observed in some plants of PI 185410 and PI 323440, when tested to biotype L at 25°C (Cambron, Ohm, Patterson, unpublished data, 1995), but this response was not observed in any of the PI lines to any of the fly populations in tests reported here at 18°C.
Genetic Plant Necrosis Problems
There are three plant necrosis genotypes, Ne1Ne1 ne2ne2, ne1ne1 Ne2Ne2, and the double recessive. When crosses are made between the two dominant genotypes, the heterozygous plant develops leaf necroses at about the three- or four-leaf stage and usually dies before reproduction. There are several Ne-alleles described by Zeven (1971) as weak, moderate, or strong. Many of the durum wheat sources resistant to Hessian fly come from regions where Ne1 genes predominate although noncarriers (double recessives) also occur (Zeven, 1971). Ne2 carriers predominate among wheat cultivars in the eastern, soft red winter wheat region of the USA.
In using unknown Ne-gene genotypes in a genetic or breeding study, one is prudent first to make one or two crosses to a noncarrier type before crossing to a line which may be a carrier of Ne1 or Ne2. In our genetic research at the durum level, we have used the spring semidwarf durum germplasm line North Dakota D6647 (CI 15329, Lebsock et al., 1972) as the recurrent parent in backcross and testcross analyses of resistance to Hessian fly. We found it to be a noncarrier of dominant Ne-genes and susceptible to all biotypes of Hessian fly to which it has been tested. The semidwarf height results in better standing ability in greenhouse culture.
In genetic studies with common wheat, we found that winter wheat cultivars Newton (CI 17715) and Knox (CI 12798) were noncarriers of dominant Ne-alleles and were susceptible to all biotypes of Hessian fly to which they were tested. Recently, R. H. Busch (see acknowledgments) suggested the spring wheat cultivar Len (CI 17790) as a noncarrier. We found it to be susceptible to all biotypes of Hessian fly that we maintain. As a spring wheat recurrent parent, we can cycle more generations per year than with winter wheat cultivars.
Utilizing Resistance from Durum Wheat
There appear to be many potentially useful sources of resistance to the changing populations of Hessian fly in eastern USA among the 26 durum wheat lines observed in our tests. The lines with resistance conditioned by single genes could be utilized more quickly.
We believe that the most effective approach for using genes for resistance to Hessian fly from these durum germplasm lines is to isolate single genes conditioning resistance in durum or common wheat so that the resistance can be thoroughly studied for effectiveness against different biotypes and populations of Hessian fly. The identification of markers for the genes would provide efficient and practical tools for pyramiding two or more genes in a cultivar to provide long-term effectiveness of the resistance to Hessian fly. DNA markers for eleven genes for resistance are available, including one for the very effective H13 (Dweikat et al., 1997). Since the effectiveness of a gene for resistance to Hessian fly is sometimes somewhat different in durum and common wheat, preference for the analysis should be at the ploidy level of anticipated use in breeding resistant cultivars.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Received for publication August 23, 2001.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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This article has been cited by other articles:
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  H.W. Ohm, F.L. Patterson, R.H. Ratcliffe, S.E. Cambron, and C.E. Williams Registration of Hessian Fly Resistant Wheat Germplasm Line P921696 Crop Sci., November 1, 2004; 44(6): 2272 - 2273. [Full Text] [PDF]
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