Submitted to: International Journal of Plant Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/17/2009
Publication Date: 1/1/2010
Publication URL: www.pagepress.org/journals/index.php/pb/article/viewFile/pb.2010.e3/1781
Citation: Guo, B., Butron, A., Scully, B.T. 2010. Maize silk antibiotic polyphenol compounds and molecular genetic improvement of resistance to corn earworm (Helicoverpa zea Boddie) in sh2 sweet corn. International Journal of Plant Biology. 1(e3):13-18. Interpretive Summary: Host-plant resistance to ear-feeding insects has been identified and characterized as largely due to high maysin in the silks. Insects of corn earworm damage corn crop worldwide by directly consuming kernels and by introducing ear-rotting fungi such as Aspergillus flavus and Fusarium moniliforme that may result in mycotoxin contamination. Sweet corn is one of the highest ranking vegetable crops in the U.S. in terms of both market value and total acreage. Pesticide is also used intensively in the production of sweet corn due to consumer demand for zero damage to ears. As a result, growers in the South totally depend on scheduled pesticide applications to control ear-feeding insects. The mapping technology provides a powerful tool for dissection of quantitatively inherited traits. Molecular marker-assisted selection can overcome the difficulties of conventional breeding. We have been involved in a breeding program to transfer resistance to the corn earworm in sh2 sweet corn, and the genetic markers controlling over the chemicals, maysin, apimaysin, methoxymaysin, and chlorogenic acid in the silks, have been characterized. We demonstrated that a gene, P1, from the field corn, which was lost in the development of sweet corn, has a strong interaction with a1 gene in sweet corn on these chemical productions. We used these two genes as markers in breeding selection from selfed backcrosses for individuals with homozygous recessive a1 from sweet corn and dominant P1 (from field corn), resulting in much higher antibiotic chemical compounds in the silks than the donor parental line. The results suggest that transferring the resistance may be an alternate strategy for control of corn earworm damage in sweet corn without the extensive use of pesticide.
Technical Abstract: The flavor of sh2 super-sweet corn is preferred by consumers. Unfortunately, sh2 sweet corn has very little genetic variation for resistance to insects. This presentation will review and summarize the studies of the functions of two loci, p1 and a1. The P1 allele can have a major role in the resistance of sh2 sweet corn to corn earworm, an allele that was lost in the historical development of sweet corn because of its pleiotropic effect on the undesirable cob color and silk browning. The P1 allele has significant effects on biosyntheses of silk antibiotic compounds, maysin, apimaysin, methoxymaysin, and chlorogenic acid. Therefore, improvement of chlorogenic acid and AM-maysin (apimaysin and 3’-methoxymaysin) may be important to the capacity of host plants’ resistance to insects when individuals have substantial amount of these minor compounds. The effect of a1 gene shows dominant gene action for low maysin and significant epistatic gene action with p1 gene. The dominant functional allele A1 causes anthocyanin pigments to form in the aleurone, plant, and pericarp tissues, the recessive nonfunctional a1 allele causes absence of pigment (colorless) in these tissues. The presence of maysin and its analogues with antibiotic activity in silks is an important defense against invasion of the ear by corn earworm. A thorough knowledge of the inheritance of these compounds will assist breeders in choosing the most efficient method of incorporating this trait into elite sweet corn inbred lines. If silk browning and cob color are critical factors for maysin production in sweet corn but lacks customer’s preference, then separating the red cob and browning silk, which are controlled by the P1 allele, may be difficult, if not impossible. There are some field corn germplasm with p1-wwr alleles (clear pericarp, white cob, browning silks), but the amount of antibiotic flavones and their potential as a donor need further investigation.