Divergent Selection for Vegetative Phase Change in Maize and Indirect Effects on Response to Puccinia sorghi

Abstract

In maize (Zea mays L.), some experiments have indicated that early vegetative phase transition is associated with increased resistance to disease, insects, and stalk lodging. The sweet corn population Minn11 was selected over three cycles of divergent recurrent selection for early‐phase transition and late‐phase transition. Objectives were to determine the effectiveness of divergent recurrent selection and if the divergent selection program was associated with resistance to common rust (Puccinia sorghi). Selection resulted in a significant linear response for last leaf with juvenile wax in both the early and late directions of selection. The third cycle in the late direction (C3L) had two more leaves with juvenile wax than cycle zero (C0). The third cycle in the early direction (C3E) had 1.5 fewer leaves with juvenile wax than C0. To determine the effects of divergent selection for vegetative phase change on response to common rust the populations were inoculated with rust at three developmental times, vegetative stage (v) 5, v10, and v15, and rust damage was rated on leaves 7 through 13 individually, resulting in 21 potential responses for each direction of selection. Among the 21 leaf by developmental stage combinations, there were 9 significant linear trends in the late direction of selection. Most of the linear trends were detected in leaves 7 through 9. Selection for early transition did not affect response to common rust. The amount of leaf area damaged by rust in C3E never differed from the amount in C0.

Vegetative Phase Change Characteristics and Resistance to Common Rust of Corn Cultivars Developed in Different Eras

“…The lack of a correlation between LLJW and rust damage agrees with the fi ndings of Abedon and Tracy (1998) and Chandler and Tracy (2007), but it is in contrast to the fi ndings of , Basso et al (2008), and Riedeman et al (2008), who found a signifi cant correlation. Overall, none of the phase change measurements were correlated with any of the non-phase change traits.…”

Divergent Recurrent Selection for Vegetative Phase Change and Effects on Agronomic Traits and Corn Borer Resistance

“…and European corn borer ( Ostrinia nubilalis Hubner) are common yield‐reducing factors in maize (Dicke and Guthrie, 1992; Smith and White, 1992). The relationship between adult vegetative tissue and common rust resistance was demonstrated by Abedon and Tracy (1996) and Basso et al (2008) Resistance to insects such as European corn borer, fall armyworm ( Spodoptera frugiperda J.E. Smith), and southwestern corn borer ( Diatrea graniosella ) has also been linked to vegetative phase change (Lawson and Poethig, 1995; Abedon and Tracy, 1996; Williams et al, 1998, 2000).…”

General Resistance in Maize to Southern Rust (Puccinia polysora Underw.)

“…Mutant genes such as glossy and corngrass delay the transformation to cuticular wax and appeared to delay expression of resistance to common rust (Abedon and Tracy, 1996). Basso et al (2008) inoculated common rust at different stages of leaf development in populations selected for early vs. late change to the cuticular wax and also suggested their association with timing and severity of rust infection. We could not confirm this type of behavior for southern rust in Hawaii, including mutants for glossy and corngrass .…”

“…Urediospore infection by rusts requires extended dew periods and is evidently affected by the manner in which water films occur on grass leaves. Tracy and colleagues (Abedon and Tracy, 1996; Basso et al, 2008) have researched leaf waxes and suggested their relationship to rust tolerance. Young corn leaves (first 5 to 8) have an epicuticular wax that causes water to bead up in tiny droplets while mature leaves have a star‐shaped cuticular wax that causes water to spread in a thin, rapidly drying film that ostensibly might inhibit rust infections.…”