J. Scott Armstrong1, Gary Peterson2, Bill Rooney3   Screening for Host Plant Resistance to the Sugarcane Aphid In Grain Sorghum J. Scott Armstrong1, Gary Peterson2, Bill Rooney3 United States Department of Agriculture - Agricultural Research Service 1USDA, ARS, Wheat, Peanut and Other Field Crops Research Unit, Stillwater, OK; 2 Texas AgriLife Research and Extension Center, Lubbock, TX ; 3 Department of Soil and Crop Sciences, Texas A&M University, College Station, TX RESULTS AND DISSCUSSION The top ten sorghum entries that were below a damage rating of 6 are shown in comparison to the susceptible TX2737, which is GB biotype C resistant, but has no defense against SCA (Fig.2). The GB C and E resistant TX2783 showed a high level of phenotypic resistance as did B11055. Entries 11LI5051,52 (TX2952) and BL11070 sustained chlorotic damage greater than a 3 but less than 4, and also show a high level of resistance. Other entries below a damage rating of 6 were 12LI7291 (Ent62/SADC), 10LI1090 (SV1*Sima), 12LI7281 (TAM428), B11040-WF2, 10LI1092 (MACIA*TAM428), and B12018. These last entries show good phenotypic resistance considering the aphid pressure they were under during this screen. Plant height was negatively correlated to phenotypic resistance in that the lower damage ratings resulted in taller plants (Fig 3.), realizing that phenotypic differences in plant height exist even among non-infested entries. For example the SV1*SIMA (10L1090) is a very tall sorghum genotype when compared to the others despite being infested with SCA. However, the SCA injury in the seedling stage will influence plant height to a greater extent than will the inherent plant height potential based on our experience from conducting these assays. Cross resistance is sustained TX2783, possibly by the GB resistance E gene, in that the C resistance is in both TX2737 and TX2783 does not appear to confer resistance. Further investigation is needed to confirm this. One line that did not make the top 10 in terms of damage rating was TX2791 which is resistant to GB biotypes C, E, and I. In this instance, no cross resistance occurred in that this line sustained the highest damage rating of a 9. TAM428 is a known source of resistance evaluated in India, and has historically been in the mid-range of 5-6 in damage ratings (Sharma et al. 2013). Realizing that this is a preliminary screen, it does appear that good sources of SCA resistance can be utilized from these results. Further research efforts will screen more lines from the South African breeding program (Gary Peterson) and from those of Bill Rooney that showed very good potential as resistant sources in this preliminary screen. We will also investigate the types of resistance, although this data appears to show tolerance as the mechanism. Future screens should also seek to identify non- preference and antibiosis. INTRODUCTION The sugarcane aphid has increased in distribution into the southern United States causing economic damage to grain sorghum by infesting and increasing populations later in what might be the second half of the production season. Typically, after two years of observation, the infestations explode with sorghum plants entering the boot to heading stages. Not only is there a reduction in grain yield due to heavy infestations, but harvesting is negatively impacted because machinery, including the augers, are gummed-up from the honeydew and or aphids that are covering the plant at the time of harvest. Finding sources of host-plant resistance in grain sorghum germplasm would have a significant impact in reducing this aphid problem. We report here some of the first efforts of identifying resistant sources of grain sorghum to the sugarcane aphid. OBJECTIVES Our main objective was to evaluate known greenbug resistance sources of grain sorghum to the sugarcane aphid because they are readily available and well known, and other lines that were used in the South African breeding program (Gary Peterson) or from Bill Rooney’s breeding program. If found to be cross-resistant to both aphid pest species, sources could possibly be used immediately, or used in crossing and breeding programs to develop new lines that are more acceptable, based on geographic location and desired agronomic traits. MATERIALS AND METHODS A combined group of 46 sorghum entries were compiled from the sorghum breeders, in addition to the sorghum lines used to differentiate GB biotypes from the USDA-ARS Stillwater, OK (Table 1). The entries were replicated 16 times using the online replication program Research Randomizer (http://www.randomizer.org/), and planted on 12/31/2013 in a total of eight, 96 cell flats filled with a mixture of sand, ready-mix, and fritted clay. The experiment was infested with 20 SCA per plant on 01/06/2014 from an aphid colony originally collected from grain sorghum in Matagora County, Texas in August of 2013. The experiment was evaluated on 01/24/2014 for chlorotic feeding injury when the control plants (TX 2737) were estimated to be 90% dead using a rating scale of 1-9 scale (Webster et al. 1990). See figure 1 for more description of damage ratings. Plant height was measured at the time of damage ratings, as well as the number of leaves from each sorghum entry. Because the damage ratings are subjective, we used cut-off lines of 1-3 as highly resistant, 4-6 as moderately resistant, and 7-9 as susceptible. The discreet variables of plant height and leaf number were analyzed using ANOVA, and means were compared using LSD tests (alpha = 0.05). Fig. 1. Sorghum damage rating (1-9 scale) upper left (A) represents a rating of 2, upper center (B) represents a rating of 4, and upper right center plant (C) represents a 9, lower images of the evaluation flats (D & E) showing heavy infestations and damage to sorghum entries. Fig. 2. Damage ratings for the top ten entries evaluated for chlorotic feeding injury including the susceptible TX2737. The red numbers within the bottom of each bar are the entry numbers from the total of 46 that were used in the experiment. Table 1. Sorghum germplasm used to screen for host plant resistance to the sugarcane aphid. Entry Germplasm Pedigree Resistance/ Susceptibilty 1 10LI6041 RTx2791 (GB resist. from PI550607) 2 11LI5034 RTx430   3 12LI7281 TAM428 SCA resist. in South Africa 4 12LI7291 Ent62/SADC 5 10LI1111 (9MLT176/(MR112B-92M2)*Tx2880)*A964)-LG8-CABK-LBBK-LGBK-LGBK 6 10LI1099 (Dorado*Tegemeo)-HW13-CA1-CC2-LGBK-CABK 7 10LI1104 (A964*P850029)-HW6-CA1-CC1-LGBK-CABK 8 10LI1096 (Kuyuma*BRON155)-CA5-CC1-CABK-CABK 9 10LI1092 (Macia*TAM428)-LL9 10 10LI1091 (Segeolane*WM#322)-LG2-LG2-(03)BG1-LG1-LBK-PRBK 11 10LI1093 (Macia*TAM428)-LL2 12 10LI1244 Tx7000 Suscept. to all GB 13 10LI1112 (9MLT176/(MR112B-92M2)*Tx2880)*A964)-CA3-CABK-CCBK-CABK-CABK 14 10LI1094 (LG35*WM#322)-BE40-LG1-CA1-LGBK-CABK-CABK 15 10LI1101 (Dorado*Tegemeo)-HW14-CA1-CC2-CABK-CABK 16 10LI1102 (Dorado*Tegemeo)-HW15-CA1-CC2-LG1-CABK 17 10LI1106 (5BRON151/(7EO366*GR107B-90M16)*Tegemeo)-HG1-LGBK-CABK-CABK 18 10LI1108 (5BRON151/(7EO366*GR107B-90M16)*Tegemeo)-HG7-CC2-CABK-CABK 19 10LI1090 (SV1*Sima/IS23250)-LG15-CG1-BG2-(03)BGBK-LBK-PRBK 20 10LI1095 (6BRON161/(7EO366*Tx2783)*CE151)-LG5-CG2-(03)BG1-LBK-PRBK 21 11LI6041 Tx2971 Suscept. To SCA, rest. GB C,E,I, 22 11LI5023,24 Tx436 23 10LI1187 Tx2963 24 11LI5051,52 Tx2952 25 11PR1375 86EO361 26 11PR1389 04BRON191 27 11LI6035 Tx2948 28 B10547 (BTx623/N109B) 29 B10548 30 B10584 (BTx623/BTx642) 31 B10591 (BTx642/BTXARG-1) 32 B11033 (BTxARG-1/(RTx436*P850029)-CS42..) 33 B11040-WF1 (BTxARG-1/P850029) 34 B11040-WF2 35 B11055 (BTx631/B0PR47/(GB102A*Tx631)) 36 B11070 (DL0N357/B0PR47/(GB102A*Tx631)) 37 B11078 (N623B/DLON357) 38 B11080 (N290B/BTx645) 39 B12018 (B05147-CS1-WF1-CS3/B01066-CS1-WF1) 40 B12109 42 TX 2783 GB biotype C & E ressist. 43 TX 2737 GB biotype C ressist. 44 PI 550607 GB biotype B,C,E, G & H res. 45 PI 550610 46 PI 264453 GB biotype C & E resist. References Webster, J.A., C.A.  Baker, and D. R.  Porter. 1991.  Russian wheat aphid (Homoptera:  Aphididae) Detection and mechanisms of resistance in barley. J. Econ. Entomol. 84:699-673. Sharma, H. C., S. P. Sharma, and R. S. Munghate. 2013. Phenotyping for resistance to the sugarcane aphid Melanaphis sacchari (Hemiptera: Aphididae) in Sorghum bicolor (Poaceae). International Journal of Tropical Insect Science Vol. 33, No. 4, pp. 227–238. Fig. 3. Plant height (cm) of the 46 entries used to evaluate the phenotypic response of sorghum lines to sugarcane aphid feeding injury.