A wheat cultivar with reduced root ethylene sensitivity shows improved root penetration, leaf water relations and yield in dry compact soil

Soil compaction is an increasing problem in global agriculture, causing more severe effects when soil dries. Since insensitivity to the plant hormone ethylene maintains root elongation in compact soil, wheat cultivars with reduced sensitivity to ethylene were hypothesised to have greater root and shoot growth in compact soil, and higher plant water status when this soil dried. Screening wheat cultivars revealed root-applied ethephon solution or exposure to ethylene gas inhibited root elongation of the cultivar Chewink#1 more than Kutz. These cultivars were glasshouse-grown in soil columns with a factorial combination of soil compaction and drying, and in field trials with different tillage or irrigation treatments. Although both cultivars had similar root and shoot biomass in loose soil irrespective of soil moisture, Kutz accumulated more biomass than Chewink#1 in compact soil. Greater root development of Kutz deeper in the soil profile (also occurring in field experiments) was associated with cultivar differences in water relations, as Kutz maintained higher stomatal conductance and leaf water potential, with lower foliar ABA concentration, as compact soil dried. Although further investigations with specific wheat alleles conferring ethylene sensitivity are needed, cultivars with less ethylene-sensitive root growth may grow better in compact soils, as observed in rice.