Diallel Analysis of Southwestern Corn Borer Leaf Feeding Damage in Maize 

Research Article


Diallel Analysis of Southwestern Corn Borer Leaf Feeding Damage in Maize

Corresponding author:     Dr. W. Paul Williams, Box 9555, Mississippi State, MS 39762, USA,

Tel: +1-662-325-2735; Fax: +1-662-325-8441; Email: paul.williams@ars.usda.gov


Abstract

Southwestern corn borer [Diatraea grandiosella (Dyar)] is an important pest of maize in the southern United States. It feeds extensively within the leaf whorls of plants in the vegetative stages of growth. This reduces both the quantity and quality of harvestable grain. Germplasm lines with resistance to southwestern corn borer leaf feeding have been developed and released. A diallel cross was produced by making all possible crosses among five lines selected for resistance to southwestern corn borer and five lines selected for other qualities. The lines selected for resistance exhibited significantly less damage than the unselected lines. General combining ability was a highly significant source of variation in the inheritance of resistance among these lines, but specific combining ability was not. Estimates of general combining ability effects for the five lines selected for reduced southwestern corn borer damage were highly significant indicating that these lines could be useful in developing maize hybrids that sustain less damage from southwestern corn borer

Keywords: Maize; Southwestern Corn Borer; Host Resistance; Combining Ability

Introduction

Southwestern corn borer [Diatraea grandiosella (Dyar)] is an important pest of maize (Zea mays L.), across much of the southern United States. Larvae of the overwintering generation feed extensively on the leaves within the whorls of plants in the vegetative stages of growth. Later generations feed on developing ears and ear shoots before tunneling into the stalks [1]. Southwestern corn borer feeding can significantly reduce both the quantity and quality of harvestable grain [2,3].

Host plant resistance is widely considered a desirable way to reduce losses to this pest. The U. S. Department of Agriculture’s Agricultural Research Service (USDA-ARS) at Mississippi State, Mississippi, has developed and released maize germplasm lines with resistance to leaf feeding by southwestern corn borer and fall armyworm [Spodoptera frugiperda (J. E. Smith)]. In breeding for resistance, plants in the mid-whorl stage of growth are artificially infested with neonates from a laboratory- reared colony and the resulting leaf feeding damage visually rated. Genotypes exhibiting the lowest levels of damage in successive cycles of selection are retained for line development. Survival and rate of growth tend to be lower for larvae reared on germplasm lines selected for resistance to leaf feeding than on susceptible lines [4].

This investigation was undertaken to gain information on the inheritance of resistance to southwestern corn borer in maize. A diallel cross was produced by making all possible crosses among 10 germplasm lines. Five of the lines were known to exhibit resistance to leaf feeding damage by the southwestern corn borer. The 45 resulting single crosses were infested in the mid-whorl stage of growth with southwestern corn borer neonates. Leaf feeding damage was visually rated 14 days after infestation. Specific objectives were to (1) compare leaffeeding damage sustained by germplasm lines selected for resistance to southwestern corn borer with damage sustained by lines not selected for resistance to southwestern corn borer, (2) compare leaf feeding damage sustained by crosses among the lines, and (3) obtain information on the relative importance of general and specific combining ability in the inheritance of resistance to southwestern corn borer in crosses among these lines.

Materials and Methods

Ten germplasm lines developed and released by USDA-ARS at Mississippi State were selected as parents of a diallel cross. Five of the parental lines were developed as sources of resistance to leaf feeding by southwestern corn borer: Mp707 [5], Mp708 [6], Mp713 and Mp714 [7], and Mp716 [8]. The other five parental lines were developed and released as sources of resistance to aflatoxin accumulation: Mp313E [9], Mp420 [10], Mp715 [11], Mp717 [12], and Mp719 [13]. The resulting 45 single crosses were grown in experiments planted at Mississippi State in a Leeper silty clay loam (fine montmorillonitic, nonacid, thermic Vertic Haplaquept) soil in a randomized  complete block design with four replications on 24 Apr. 2014 and three replications on 5 May 2015. Single-row plots were approximately 5 m long, spaced 1 m apart, and thinned to 20 plants. Each year, the 10 parental lines were planted in a randomized complete block design with three replications on the same dates and in adjacent areas of the field as the single crosses.

On 24 May 2014 and 4 June 2015, respectively, when plants were in the V-6 to V-7 stage of growth [14], all plots were infested with 30 southwestern corn borer neonates per plant. Fourteen days after infestation, plants were visually rated for leaf feeding damage. The rating scale used was defined as follows: 0 = no visible leaf damage; 1 = small amount of pin-hole damage; 2 = small amount of shot-hole damage on a few leaves; 3 = shot-hole damage on several leaves; 4 = shot-hole damage and elongated lesions on a few leaves; 5 = elongated lesions on several leaves; 6 = several leaves with 25 mm lesions; 7 = long lesions on 50% of the leaves; 8 = long lesions on 70% of the leaves; and 9 = long lesions on most leaves.

Plot means for leaf feeding damage ratings were calculated and used in the analysis of variance. Data for both the parental lines and the single cross hybrids were analyzed both within years and combined over years. Means were compared using the Least Significant Difference procedure. For the combined analysis, years were considered random, and genotypes were considered fixed effects. The diallel analysis was performed using the SAS General Linear Models procedure [15]. The variance was partitioned using DIALLEL-SAS [16,17], based on Griffing’s Method 4, Model I [18], into general (GCA) and specific (SCA) combining ability components. To test mean squares for the GCA and SCA components for significance in the two-year analysis, the interaction between years and the corresponding components were used as the error terms for F tests. Estimates of GCA and SCA effects were calculated and their significance was determined by t tests.

Results and Discussion

The inbred lines sustained heavier leaf feeding damage in 2015 than in 2014 (Table 1). The five germplasm lines developed as sources of resistance to southwestern leaf feeding damage.

†S Indicates susceptibility to leaf feeding damage and R indicates resistance to leaf feeding damage.

‡Plants at the V-6 to V-7 stage of growth were infested with 30 southwestern corn borer larvae, and damage was rated 14 days later on a scale of 0 (no damage) to 9 (extensive damage).

Exhibited significantly less damage than the other lines in both years. In 2014 the resistant lines averaged 3.2 indicating only shot-hole damage on several leaves. The other five lines averaged 7.1 indicating long lesions on several leaves. In 2014, Mp708 and Mp714 had the least damage and Mp420 the heaviest damage. In 2015, Mp716 sustained the least leaf damage with a rating of 4.2, and Mp708 and Mp714 rated only slightly higher at 4.5.

There were significant differences between years and among single cross hybrids in both 2014 and 2015 (Table 2).The hybrids sustained heavier damage in 2014 than in 2015 (Table 3). Mp420 × Mp717 sustained the most extensive damage in both 2014 and 2015, 8.0 and 7.4, respectively. Mp708 × Mp713, Mp708 × Mp714, and Mp714 × Mp716 sustained the least damage in 2014 with ratings of 3.5. Mp704 × Mp707 with a rating of 4.0 was the least damaged single cross in 2015.

†GCA, general combining ability; SCA, specific combining ability

‡df = 132 in 2014, 88 in 2015, and 220 for combined years.

The analysis of the diallel cross indicated that GCA was a significant source of variation each year and in the analysis  combined over years (Table 2). SCA was not a significant source of variation in either year or in the combined analysis for resistance to southwestern corn borer leaf damage. The interactions of both GCA and SCA with years, however, were highly significant. Estimates of GCA effects associated with the parental lines (Table 4) are consistent

†S Indicates susceptibility to leaf feeding damage and R indicates resistance to leaf feeding damage.

‡Plants at the V-6 to V-7 stage of growth were infested with 30 southwestern corn borer larvae, and damage was rated 14 days later on a scale of 0 (no damage) to 9 (extensive damage).

With the levels of southwestern corn borer damage sustained by the inbred lines per se (Table 1). Estimates of GCA effects for the lines developed and released as sources of resistance to aflatoxin accumulation and not specifically for resistance to southwestern corn were significant and positive (Table 4). This indicates that these lines contribute to hybrids with increased.

Susceptibility to southwestern corn borer damage. GCA effects associated with the five parental lines that had been developed and released as sources of resistance to leaf feeding by southwestern corn borer and fall armyworm were highly significant and negative. This indicates that all of the lines selected for resistance contribute to reduced levels of southwestern corn borer damage in hybrid combinations. Previous studies have indicated that lower levels of leaf feeding damage are associated with reduced survival and a slower rate of growth of southwestern corn borer larvae feeding on the resistant germplasm [2,4]. Plants sustaining high levels of leaf feeding damage are more likely to be stunted and lower yielding than resistant plants. Mp707, Mp708, Mp713, Mp714, and Mp716 could be useful as sources of resistance in breeding for reduced southwestern corn borer damage. Breeding strategies such as recurrent selection based on S1 progeny performance that take advantage of GCA should be most effective in developing breeding lines and populations with higher levels of resistance to southwestern corn borer.

Conclusions

The analysis of variance of the diallel cross indicated that GCA was a highly significant source of variation in the inheritance of resistance to southwestern corn borer, but SCA was not a significant source of variation. Estimates of GCA indicated that Mp707, Mp708, Mp713, Mp714, Mp716 could be useful in developing germplasm and populations with higher levels of resistance to southwestern corn borer leaf feeding damage.

Acknowledgements

Funding for the research was provided by the United States Department of Agriculture’s Agricultural Research Service. The authors express their appreciation to Susan H. Wolf for excellent technical assistance. This paper is a joint contribution of USDA-ARS and the Mississippi Agricultural and Forestry Experiment Station. Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by USDA.

 References

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