An increased wheat yield potential under changing environmental conditions is a challenge in agriculture. Resistant wheat lines can yield more than susceptible wheat lines in the presence of Russian wheat aphid infestation. There are currently four Russian wheat aphid (RWA) biotypes known in South Africa with different virulence against different wheat cultivars. To keep up with the ever-changing patterns it is necessary to screen the cultivars for resistance against these Russian wheat aphid (RWA) biotypes. All the dryland wheat cultivars on the market were evaluated for resistance against the four known Russian wheat aphid (RWA) biotypes in South Africa. Through this evaluation, the status of Russian wheat aphid (RWA) resistance in South African dryland wheat cultivars can be updated to adapt to environmental changes and the wheat industry can adapt to changes in virulence of Russian wheat aphid (RWA) biotypes that may cause damage to Russian wheat aphid (RWA) resistant cultivars, subsequently affecting yield. Evaluations were done in the glasshouse by screening wheat cultivars against four different South African Russian wheat aphid (RWA) biotypes, RWASA1-RWASA4, under controlled conditions. The glasshouse evaluations showed that out of the 19 dryland wheat cultivars currently on the market in South Africa 16 are resistant against RWASA1, 7 are resistant against RWASA2, 7 are resistant against RWASA3 and 5 are resistant against RWASA4. Dryland wheat cultivars were also evaluated under field conditions at four different field localities. In the field, 5 cultivars were resistant to RWASA3 at two localities, respectively, and 3 and 5 cultivars were resistant to RWASA4 at two localities, respectively. Since Russian wheat aphid (RWA) damage can influence the final yield of a wheat cultivar significantly, changing conditions can influence both resistant cultivars, and the virulence of Russian wheat aphid (RWA). It is advisable to evaluate wheat cultivars on the market under different conditions and with all known Russian wheat aphid (RWA) biotypes in an area.
Wheat yield is one of the most important factors to consider by wheat producers and increased yield under changing conditions is a priority in wheat breeding. Biotic factors can influence the final yield significantly and managing the ecology, distribution, virulence patterns, and variability of pests and diseases may minimize the gap between actual and attainable yields. The Russian wheat aphid (RWA), Diuraphis noxia, is a serious pest to small grain production throughout the world. The economic impact from this pest can be considerable and has been estimated at $893 million for 1987-1993 in the Western United States [
There are currently 19 dryland wheat cultivars on the market in South Africa. These cultivars were screened against four RWA biotypes (RWASA1 - RWASA4) in the glasshouse using the bioassay developed by Du Toit [
To avoid the bias that may be associated with screening under artificial conditions the 19 dryland wheat cultivars on the market in South Africa were evaluated in the field. The cultivars were planted on 29/06/2017 in 5 m × 5 row plots at 4 different localities in the Free State. All of these localities lies in the summer rainfall area of South Africa: Clarens (GPS: S28˚23.913'E28˚25.760'; average annual rainfall―764 mm; average annual temperature―13.7˚C), Clocolan1 (GPS: S28˚59'15.51"E27˚40'06.52"; average annual rainfall―635 mm; average annual temperature―14.9˚), Clocolan2 (GPS: S29˚00'03.98"E27˚38'12.91"; average annual rainfall―635 mm; average annual temperature―14.9˚) and Ficksburg (GPS: S28˚47.556'E27˚57.917'; average annual rainfall―621 mm; average annual temperature―15.1˚C). The trial layout was a randomized complete block design with four replications. Data were collected from the middle rows to avoid border effects. The cultivars were evaluated in the field on 30/10/2017 at adult stage on a 1 - 4-point scale where 1―no damage: Escape/Resistant (R); 2―chloretic spots on leaves: Resistant (R); 3―longitudinal striping on leaves: Medium susceptible (S); 4―rolling of leaves: susceptible (S).
RWA samples were collected at each locality and the biotype for the locality was determined. A single female aphid from each sample collected in the field was transferred to a wheat plant and caged (gauze size: 315 micron) to produce a clone colony. The biotype of each RWA clone was determined by screening its feeding damage on 11 previously established plant resistant sources containing designated resistance genes Dn1 to Dn9 and Dnx and Dny (
Russian wheat aphid damage rating across all cultivars were analysed using a two-way (damage rating, cultivar) analysis of variance (ANOVA). Mean damage
South African Biotypes | |||||
---|---|---|---|---|---|
Wheat genotype | Resistance gene | RWASA1 | RWASA2 | RWASA3 | RWASA4 |
CO03797 | Dn1 | R | S | S | S |
CO03804 | Dn2 | S | S | S | S |
CO03811 | Dn3 | S | S | S | S |
Yumar | Dn4 | R | R | S | S |
CO9500043 | Dn5 | R | R | R | S |
CO960223 | Dn6 | R | R | R | R |
94M370 | Dn7 | R | R | R | R |
Karee-Dn8 | Dn8 | R | S | S | S |
Betta-Dn9 | Dn9 | R | S | S | S |
PI586955 | Dnx | R | R | R | R |
Stanton | Dny | R | R | S | S |
R = RWA resistant; S = RWA susceptible.
rate entries with significant (P < 0.05) clone-by-plant interactions were separated by Fisher’s protected least significant difference (LSD) test at the 5% level.
RWASA4 is the most virulent South African biotype and of the known genotypes only the ones containing the Dn6, Dn7 and Dnx genes have adequate resistance against this biotype ( [
RWA biotypes with different virulence patterns against current wheat cultivars on the market occur in different wheat production areas in South Africa. It is therefore important to determine the virulence of the different biotypes against cultivars on the market in order to make recommendations as to which cultivar has resistance to a biotype occurring in a specific area. Glasshouse screening of the dryland cultivars in South Africa showed that the wheat cultivars have different resistant and susceptible reactions to the four different biotypes (
Evaluation under controlled conditions in the glasshouse gives us a guideline of resistance of wheat cultivars against the four different RWA biotypes.
RWASA1 | RWASA2 | RWASA3 | RWASA4 | |
---|---|---|---|---|
ELANDS | 4.33bc | 8.76a | 7.43bcd | 8.33a |
GARIEP | 4.38bc | 8.71a | 7.72abc | 8.33a |
KOONAP | 4.00cdef | 9.00a | 7.81abc | 7.71abc |
MATLABAS | 4.00cdef | 8.10ab | 7.09cd | 7.81ab |
SENQU | 4.19cde | 9.00a | 6.95cde | 8.05ab |
PAN3111 | 8.76a | 8.90a | 8.667ab | 8.71a |
PAN3118 | 8.95a | 8.67ab | 9.00a | 9.00a |
PAN3120 | 8.86a | 8.86a | 9.00a | 9.00a |
PAN3161 | 3.33ef | 4.14e | 4.05hi | 5.95bcdef |
PAN3195 | 4.093cde | 9.00a | 4.14hi | 5.29ef |
PAN3198 | 4.00cdef | 7.67abc | 7.28bcd | 7.00abcde |
PAN3368 | 4.47cde | 4.00e | 4.43ghi | 4.8f |
PAN3379 | 3.43def | 4.29e | 4.00hi | 4.00f |
SST316 | 3.95cdef | 6.19d | 6.86cde | 8.29a |
SST317 | 4.33bc | 6.34cd | 6.10def | 7.81ab |
SST347 | 4.14cde | 6.09d | 4.81fghi | 7.00abcde |
SST356 | 5.14b | 8.81a | 7.19cd | 7.48abcd |
SST374 | 3.14f | 4.52e | 3.52i | 5.52def |
SST387 | 3.67cdef | 7.29bcd | 7.43bcd | 7.05abcde |
LSD (5% level) | 0.8660 | 1.397 | 1.444 | 2.141 |
Means within a column followed by the same lowercase letter are not significantly different (P > 0.0001).
During 2017 there was a high natural infestation of Russian wheat aphid at the trial sites at Clarens, Clocolan and Ficksburg. This resulted in noticeable damage symptoms on both RWA susceptible and resistant cultivars. Screening of RWA samples collected at the field localities showed that the dominant RWA biotype at Clocolan1 and Clocolan2 was RWASA3 and at Clarens and Ficksburg was RWASA4. In the field at Clocolan1 5 cultivars were resistant (RWA damage score < 3) to RWASA3; at Clocolan2 5 cultivars were resistant to RWASA3; at Ficksburg 3 cultivars were resistant to RWASA4 and at Clarens5 cultivars were resistant to RWASA4. The cultivars in the field showed a different susceptible/resistant reaction compared to the cultivars screened in the. In the field SST387 showed resistance against RWASA3 and RWASA4 (
Locality | Clocolan1 | Clocolan2 | Ficksburg | Clarens |
---|---|---|---|---|
Biotype | RWASA3 | RWASA3 | RWASA4 | RWASA4 |
ELANDS | 3.25ab | 3.25ab | 3.25ab | 4.00a |
GARIEP | 3.25ab | 3.50a | 3.50a | 3.50a |
KOONAP | 3.25ab | 3.75a | 3.75a | 3.00a |
MATLABAS | 3.25ab | 3.75a | 3.75a | 3.25a |
SENQU | 3.50ab | 3.00ab | 3.00ab | 3.50a |
PAN3111 | 3.50ab | 3.00ab | 3.00ab | 3.50a |
PAN3118 | 3.25ab | 3.75a | 3.25ab | 3.25a |
PAN3120 | 3.50ab | 3.75a | 3.75ab | 3.50a |
PAN3161 | 3.50ab | 3.25ab | 3.25ab | 2.75ab |
PAN3195 | 3.75a | 3.25ab | 3.25ab | 2.50b |
PAN3198 | 3.50ab | 3.00ab | 3.00ab | 2.50b |
PAN3368 | 2.00b | 2.75ab | 3.75a | 2.50b |
PAN3379 | 2.00b | 2.75ab | 2.75ab | 3.50a |
SST316 | 3.25ab | 3.25ab | 3.25ab | 3.50a |
SST317 | 3.00ab | 3.25ab | 3.25ab | 3.25a |
SST347 | 2.25ab | 2.75ab | 3.50a | 3.25a |
SST356 | 3.5ab | 3.00ab | 3.00ab | 4.00a |
SST374 | 2.25ab | 2.75ab | 2.00b | 3.00a |
SST387 | 2.25ab | 2.75ab | 2.75ab | 2.75ab |
LSD (5%) | 1.52 | 1.37 | 1.37 | 1.62 |
Means within a column followed by the same lowercase letter are not significantly different (P > 0.0001).
as drought and high temperatures. These environmental conditions can influence the expression of resistance in the plant, while it can also influence the population pressure of the RWA and consequently the damage to the plant. Macedo et al. [
The development of germplasm with adequate and lasting resistance against pests and diseases in wheat is of importance to wheat producers to reach the desired yield with less costly inputs. To achieve this objective it is necessary to screen existing wheat cultivars to ensure that these cultivars have adequate resistance against the RWA biotypes prevalent in the areas where these cultivars are planted. Glasshouse screening under controlled conditions is useful to determine levels of resistance, but is not necessarily a reflection of RWA resistance expressed in the field. It is therefore also necessary to do field evaluations in different areas to determine the expression of resistance under different conditions. Natural enemies, temperature, moisture, wind, soil type, host quality are all variables that will have an influence on RWA population growth and as a result pest pressure. The prevalent RWA biotype will also differ in different areas. This is necessary to keep pace with changes in pest virulence resulting from fluctuating environments.
The author declares no conflicts of interest regarding the publication of this paper.
Jankielsohn, A. (2019) Evaluation of Dryland Wheat Cultivars on the Market in South Africa for Resistance against Four Known Russian Wheat Aphid, Diuraphis noxia, Biotypes in South Africa. Advances in Entomology, 7, 1-9. https://doi.org/10.4236/ae.2019.71001