Leaf structural traits mediating pre-existing physical innate resistance to sorghum aphid in sorghum under uninfested conditions

Authors: TRIPLETT, ETHAN - Texas Tech University; Hayes, Chad; Emendack, Yves; LONGING, SCOTT - Texas Tech University; MONCLOVA, CECILIA - Texas Tech University; SIMPSON, CATHERINE - Texas Tech University; LAZA, HAYDEE - Texas Tech University

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2023
Publication Date: 7/20/2023
Citation: Triplett, E., Hayes, C.M., Emendack, Y., Longing, S., Monclova, C., Simpson, C., Laza, H. 2023. Leaf structural traits mediating pre-existing physical innate resistance to sorghum aphid in sorghum under uninfested conditions. Planta. 258. Article 46. https://doi.org/10.1007/s00425-023-04194-0.
DOI: https://doi.org/10.1007/s00425-023-04194-0

Interpretive Summary: The sugarcane aphid (SCA) has recently developed into a major pest in sorghum in North America and has created significant problems for the sorghum grain and forage industries by reducing yields and inhibiting grain and forage harvest. To date, the identification of sorghum lines tolerant to SCA is based on infesting seedlings with aphids and visually observing survivability in specialized and well-protected insect screening chambers. Scientists from ARS and Texas Tech University have conducted research to identify leaf structural characteristics of aphid tolerant and resistant lines. Specific leaf traits where identified which could be use to screen for SCA tolerance without infesting seedlings. This approach will enable sorghum breeding programs to quickly and easily characterize their germplasms for SCA tolerance without using the complex screening chambers only found in specific laboratories working on insects and other small pests. This data will be of particular interest to the sorghum breeding community and producers at large.

Technical Abstract: The sugarcane aphid (SCA) can severely reduce the yield potential by =60% (van Rensburg 1973, van den Berg 2002, Uyi et al. 2023). The contribution of structural traits to SCA resistance have not been extensively studied. Moreover, the current screening method is inherently subjective and requires infestation. Quantifying the micro-anatomical basis of innate SCA resistance is crucial for developing reliable screening tools that require no infestation. The goal of this study was to identify structural traits potentially linked to innate SCA resistance in sorghum. Arranged in a randomized complete block design, two SCA resistant (R.TxLBK1 and R.Tx2783), and two SCA susceptible (R.Tx7000 and R.Tx430) uninfested sorghum lines were analyzed in controlled environment and field studies. Samples from the controlled environment were collected at the fifth true leaf stage to measure: leaf thickness, epidermal cell wall thickness, cuticle thickness, intercellular width, mesophyll cell area, and chloroplast/mitochondria abundance and ultrastructure using light and transmission electron microscopy. Samples from the field study were collected at physiological maturity (139 days after planting) to measure the density and size of trichomes and stomata using scanning electron microscopy. The results showed a significant difference in stomata density, trichome density, trichome lengths, leaf thickness, mesophyll cell area, chloroplast distribution, and intracellular space. Stomata density, trichome density, trichome lengths, and chloroplast distribution were responsible for the most observed variation. Although validation is necessary, these key traits may assist in the development of an objective method of screening SCA resistance in sorghum.