Evaluation of combining ability in expired plant variety protection maize lines for Southern US adaptation and aflatoxin resistance

Abstract

Contamination of maize (Zea mays L.) grain with aflatoxin, produced by the fungus Aspergillus flavus, is a major concern in Southern US environments. Development of adapted hybrids with genetic resistance to aflatoxin accumulation is one strategy to mitigate this problem. Crossing inbred lines with recently expired plant variety protection (ex-PVP) provides a new, relatively untested, source of germplasm with improved agronomic traits to utilize in breeding aflatoxin-resistant hybrids. This study assessed the combining abilities of 32 ex-PVP lines and six aflatoxin-resistant USDA-Agricultural Research Service (ARS) lines in four environments for yield, agronomic traits, and aflatoxin. USDA-ARS lines Mp313E, Mp715, and Mp717 had positive general combining ability (GCA) for anthesis, silking, and plant height, resulting in later maturing, taller hybrids, though many had low aflatoxin. Mp717 consistently demonstrated negative GCA for aflatoxin level. The USDA-ARS line GT1309 had negative GCA for flowering time and plant height. Ex-PVP lines from both major US heterotic groups (PHGV6, PHJ65, PHM57, LH195, F118, FBLL, LH200, LH236, and PHMK0) demonstrated a favorable combination of GCA for yield, ear rot resistance, and/or reduced aflatoxin when crossed with the USDA-ARS lines. Among tested hybrids, Mp717 × PHMK0 had positive specific combining ability (SCA) for yield and negative SCA for aflatoxin level, suggesting that PHMK0 is a promising ex-PVP inbred to use in second-cycle breeding.