Evaluation of A3 cytoplasmic male sterile forage sorghum lines for resistance to sugarcane aphid

Main conclusion Three known sugarcane aphid-resistant pollinator parents were sterilized in A3 cytoplasmic male sterility and were confirmed in this study to be resistant to sugarcane aphid allowing for the development of sugarcane aphid-resistant forage hybrids. We utilized A3 cytoplasmic male sterility and converted known sugarcane aphid-resistant sorghum TX 2783, and newly released R. LBK1 (Reg. No. GP-865, PI 687244) and R. LBK2 (Reg. No. GP-866, PI 687245) into A3 sterility to determine if the sterile counterparts would also equally express tolerance and or antibiosis to sugarcane aphid. Free-choice flat screen trials and life-table demographic studies were utilized and compared to know susceptible/fertile entries KS 585, and TX 7000, and known resistant/fertile entries TX 2783 and DKS 37-07. The R. LBK1 fertile entry was more tolerant than the known susceptible entries KS 585 and TX 7000, but was not as resistant as the other resistant entries, sustaining a damage rating of 6.0 across two different screen trials. The sterile A3 R. LBK2 showed a greater tolerance and expressed higher levels of antibiosis during aphid reproductive studies when compared to the known resistant and fertile TX 2783. All other fertile (R. LBK2, TX2783) and the A3 male sterile counterparts (A3 R. LBK2, A3 TX2783) were very similar in expression of high levels of tolerance and exhibited statistically similar damage ratings of 3.3-4.3 when exposed to sugarcane aphids. No entry, either fertile or sterile, was as tolerant as DKS 37-07, a known resistant commercial hybrid. Other plant measurements including percent loss in chlorophyll content, difference in plant height, and number of true leaves for sugarcane aphid infested versus non-infested were very consistent and highly correlated with damage ratings. Antibiosis was also exhibited in both fertile and sterile versions of the resistant lines. There was a 2 x reduction in fecundity between the R. LBK1 fertile and its sterile A3 R. LBK1 when compared to the susceptible KS 585 and TX 7000; however, the remaining fertile and sterile entries had 3.8 x to 5.8 x decrease in fecundity when compared to the susceptible KS 585 and TX 7000. Other measurements in life-table statistics such as nymphs produced/female/d, and the intrinsic rates of increased were significantly lower for all fertile and sterile lines, showing that antibiosis significantly affected sugarcane aphid reproduction. In conclusion, the A3 cytoplasmic male sterility shows consistency for maintaining the single dominant trait SCA-resistant trait of TX 2783 for expressing both antibiosis and tolerance, and great utility in the development of sugarcane aphid-resistant forage sorghums.

Automated summary

By converting known sugarcane aphid-resistant sorghum into A3 cytoplasmic male sterility, we have shown that these sterile counterparts also possess tolerance and antibiosis to sugarcane aphid. This has significant implications for the development of sugarcane aphid-resistant forage sorghums.