Reaction of Two Maize Synthetics to Anthracnose Stalk Rot and Northern Corn Leaf Blight Following Recurrent Selection for Resistance to Diplodia Stalk Rot and European Corn Borer

Abstract

Nyhus, K. A., Russell, W. A., Guthrie, W. D., and Martinson, C. A. 1989. Reaction of two maize synthetics to anthracnose stalk rot and northern corn leaf blight following recurrent selection for resistance to Diplodia stalk rot and European corn borer. Phytopathology 79:166-169. Two maize (Zea mays) synthetics, BSAA and BSBB, were recurrently correlation exists between DSR resistance and ASR resistance in these selected for resistance to Diplodia (Diplodia maydis) stalk rot (DSR) and populations. NLB severity ratings were recorded on six dates throughout leaf feeding caused by the first-generation European corn borer (Ostrinia the growing season. A natural logarithm transformation was used to nubilalis) (ECB), based on the reaction of SI lines to artificial inoculations describe the disease progress curve for each of the CO to C4 populations of of D. maydis and artificial infestations of the ECB. This study was each synthetic. Linear regression of lnNLB ratings on lnDATE (days after conducted to determine if plant factors contributing to DSR and ECB inoculation) accounted for more than 97% of the variation among entries resistance also conferred resistance to anthracnose stalk rot (ASR) caused when averaged over replications. Our results showed no concomitant by Colletotrichum graminicola and northern corn leaf blight (NLB) caused improvement in NLB resistance over cycles of selection for ECB resistance, by Exserohilum turcicum. Highly significant linear improvements in ASR contradicting previous reports that 2,4-dihydroxy-7-methoxy-2H-l,4resistance were observed over cycles (CO to C4) of selection in both benzoxazin-3-one (DIMBOA), a known biochemical factor in leaf-feeding synthetics. These improvements mirrored the gains reported previously for resistance, confers resistance to NLB. DSR resistance in BSAA and BSBB and suggested that a genetic Recurrent selection has proved a useful means for maize DSR and ASR reaction. The correlation between ratings for the breeders to improve disease and insect resistance in maize two stalk rots was 0.32 for early lines and 0.26 for late lines. In populations. Recurrent selection procedures concentrate another study among 23 inbreds and 25 single crosses, correlations favorable genes for the trait or traits under selection. Populations between DSR or Gibberella stalk rot and ASR ratings ranged from improved by recurrent selection should have enhanced value as 0.36 to 0.63 (6). Although the correlations were highly significant, sources of inbred lines for hybrid maize breeding programs. they were deemed low enough to warrant separate breeding Recurrent selection has been conducted in two maize synthetics, programs. BSAA and BSBB, for resistance to Diplodia (Diplodia maydis Northern corn leaf blight (NLB), caused by the organism (Berk.) Sacc.) stalk rot (DSR) and first-generation European corn Exserohilum turcicum (Pass.) Leonard & Suggs, remains an borer (Ostrinia nubilalis HUibner) (ECB) leaf feeding. Selection important maize pest. Monogenic resistance, as well as multigenic was based on the evaluation of S lines. The most advanced cycle resistance, have been used in the control of NLB. Also, population (C4) of BSAA was significantly improved for DSR 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA) resistance but not for ECB resistance; the C4 population of BSBB has been implicated as a chemical factor involved in NLB was significantly improved for both ECB and DSR resistance (15). resistance (11-13). The relationship between DIMBOA and ECB Genetic resistances to DSR and ECB are quantitative; that is, leaf-feeding resistance is well established. DIMBOA concentrations they are conditioned by many genes, each with relatively minor in maize whorl tissue were highly correlated with field resistance effect. A genetic correlation between two pest-resistance traits ratings (8,20); DIMBOA also has been shown to cause ECB larval exists if some genes influence both traits (pleiotropy) or if genes for mortality in artificial diets (9,16). Molot and Anglade (14) each trait are inherited together on the same linkage group. Genetic compared the first-generation ECB damage ratings, the NLB correlations may be advantageous to the plant breeder and may severity ratings, and the logl10 concentration 6-methoxyenhance the usefulness of the germ plasm. benzoxalinone (MBOA, the stable breakdown product of Anthracnose stalk rot (ASR), caused by Col/etotrichumn DIMBOA) of 12 maize inbreds. The correlation coefficients for graminico/a (Ces.) G. W. Wils., is a maize disease of increasing ECB and NLB ratings with MBOA levels were -0.77 and-0.95, importance. A severe infection of ASR is characterized by black respectively, and 0.76 between ECB and NLB resistance. Other streaks on the outer surface on the stalk and discoloration of the reported significant correlations between NLB severity and pith that often extends through several internodes, starting from DIMBOA concentration were -0.61 among 13 inbreds (11) and the crown (21). C. graminicola is an aggressive pathogen, which, -0.64 among 16 inbreds (12). unlike most stalk-rotting organisms, is able to colonize living tissue The association between NLB resistance and ECB resistance has (2). Resistance to ASR also is quantitative in nature; Carson and been demonstrated only in small, fixed sets of genotypes. A much Hooker (I) identified at least five dominant genes for resistance by more extensive study of the relationship among 7,537 genotypes using reciprocal translocation testcross analysis in the inbred line over a period of 12 yr by Guthrie et al (5) has shown the A556. Other researchers have concluded that resistance to ASR correlation between NLB resistance and ECB resistance to be would not be obtained via selection for resistance to DSR or stalk 0.003. Their study found that only 1.5% of the genotypes tested rot caused by Gibbere/la. White (22) evaluated 99 inbred lines for were highly resistant to both NLB and leaf feeding by the ECB.