GEORGIA / FLORIDA
UNIVERSITY OF GEORGIA
Department of Agronomy, Griffin, GA 30212, USA.
J.W. Johnson, R.D. Barnett, G.D. Buntin, and Z. Chen.
The 2005 Georgia winter wheat crop was grown on about 200,000
planted acres, a decrease of 6 % from the previous year. Yields
of wheat grown by top producers were around 6,000 kg/ha on resistant
cultivars. The growing season was characterized by mild weather
and dry conditions during the winter and spring. A severe epidemic
of stripe rust was observed in Georgia and the lower southeastern
U.S. A major problem also occurred at harvest due to extreme
wet conditions which resulted in a high incidence of sprouting.
AGS 2010 (GA 951079-2E31) is a new cultivar developed
by the University of Georgia, derived from the cross 'GA 881130/Gore'.
The pedigree of Gore is 'Stacy/Coker 797'; the pedigree of 881130
is 'KS8998/FR 81-10//Gore'. AGS 2010 is a early-medium maturing,
white chaffed, medium-tall line that matures on average 3 days
earlier than AGS 2000 in Georgia. AGS 2010 is resistant to currently
biotypes of Hessian fly, especially Biotype L, and moderately
resistant to races of powdery mildew, and resistant to leaf rust
and stripe rust in Georgia. AGS 2010 also is resistant to WSBMV.
GA 951216-2E26 is a medium maturing, white chaffed, medium
height line that matures, on average, 2 days later than AGS 2000
in Georgia. This line is resistant to current races of leaf rust
and stripe rust in Georgia and has resistance to WSBMV. GA95121-2E26
is moderately resistant to current races of powdery mildew and
moderately susceptible to biotypes of Hessian fly. The pedigree
and history of GA 951216-2E26 is 'GA 87110*2/GA 8724'.
Scab. In the southeast region of the U.S., resistance
to FHB in local adaptive SRWW is limited. Introduction of resistant
genes from exotic sources could enhance the resistance of local
adaptive germ plasm. A Virginia line AV01W-476 with the most
widely used major QTL in chromosome 2A, 3B, and 5A for FHB resistance
was used as donor in our program. A total of 47 double-haploid
individuals were generated from backcross F1 plants induced with
maize pollen. Screening with SSR markers indicated the integration
of novel FHB resistant QTL on 3BS and 5AL from donor parents and
native adaptive gene pool of ASG2000 and its derivatives. Two
double-haploid plants from backcross of VA01W-476/GA98186 and
four double-haploid plants from backcross of 'VA01W-476/AGS2485'
were identified to have VA01W-476/W14 type QTL on 3BS and 5A.
Further evaluation for agronomic traits is under investigation.
Stripe rust. Stripe rust was very severe in 2005. We identified
effective genes as Yr17 (GA96229-3A41), Yr18 in
combination with other genes (PIO 26R61), and Yr27.
Recent studies in Georgia have found that full wheat yield could be achieved with modern adapted winter wheat cultivars while reducing seeding rates by 30 % or more. Insecticide seed treatments such as imidacloprid (Gaucho 480) can reduce aphid infestations and BYD incidence but this treatment generally is not cost effective at higher seeding rate. We conducted a study to evaluate the effect of Gaucho seed treatment at reduced seeding rates on aphid infestation, BYD incidence, wheat tillering and yield. Trials were conducted at Plains and Tifton GA over two seasons. Two cultivars, AGS 2000 and Roberts, were planted at four seed rates, 10, 20, 30, and 40 seeds/ft2 (108, 215, 323, and 430 seeds/m2) with and without Gaucho 480 at 1.5 fl oz/100 lbs seed (47 g ai/100 kg). These first-year results suggest that wheat seeding rates can be reduced without adversely affecting yield. Aphid infestations and presumably number of viruliferous aphids were not different among seeding rates but aphids/plant declined as seeding rate increased. Imidacloprid effectively controlled aphids at 30 days after planting. Conversely, BYD incidence as measured by symptomatic stems declined with increased seeding rate. Consequently, reduced seeding rates may not reduce yield potential but reduced plant populations may increase the risk of aphid infestation and BYD infection thereby making aphid control more critical.