DIMBOA（2,4dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one）是以葡萄甙（Glucoside）型態存在玉米（Zea mays L.）組織內。當組織受壓榨或在高溫下時，葡萄甙會漸次分解產生DIMBOA，DIMBOA性不穩定會再分解成MBOA（6-methozy-2-benzoxazolinone）。MBOA性穩定，因此DIMBOA在葉部組織之含量，可藉由分析定量MBOA（mg MBOA/g dry weight）而推知。化學分析結果葉部組織MBOA含量及色層分析板上MBOA亮度級數于玉米生長過程中，前者隨葉齡增長而遞減，後者隨葉齡增長而增多，顯示幼期玉米葉部組織MBOA含量較老期者為高。玉米葉部受玉米螟〔Ostrinia furnacalis(Guenee)〕為害等級及幼蟲存活數／株，以人工接種螟蟲卵塊，每株接種9個卵塊（約300卵粒／株）進行測試，試驗結果兩者均隨著葉齡增長而增多，顯示幼期玉米之抗螟性較老期者為强。供試十一玉米自交系中，以JT 30-1-1-1-15-3 及CI31A二品系在生長過程中其葉部受螟蟲為害級數及幼蟲存活數／株均較其他品系為少，同時二品系在各葉齡期之葉部組織MBOA含量亦較其他品系為高，顯示二品系具有相當程度之抗螟性。而葉部組織MBOA含量與葉部受螟害等級在第4、第6、第8、第10及第12葉齡之相關值分別為：-0.85、-0.84、-0.86、-0.82及-0.84，同時葉部組織MBOA含量與幼蟲存活數／株在以上各葉齡下之相關值依序為：-0.88及-0.83、-0.82、-0.78及-0.80，由此顯示葉部組織MBOA含量與葉部受螟害等級及幼蟲存活數／株之負相關極顯著，亦即玉米葉部組織MBOA含量越高之品系，其葉部受玉米螟為害程度及幼蟲存活數／株越少，而其抗螟性也越强，由是知DIMBOA是玉米抗亞洲玉米螟之重要化學成分而無疑。
DIMBOA Concentration in Leaf Tissue at Various Plant Growth Stages
in Relation to Maize Resistance to Asian Corn Borer
C. T. Tseng
Ching-Tien Tseng. 1996. DIMBOA Concentration in Leaf Tissue at Various Plant Growth States in Relation to Maize Resistance to Asian Corn Borer. Research Bulletin of Tainan District Agricultural Improvement Station 33: 67~81.
The chemical analytical values obtained for MBOA (6-methowy-2-benzoxazoloinone) were related to the labile cyclic hydroxamic acid precursors DIMBOA (2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one) which is formed enzymatically from its glucosides when leaf tissues are crushed or placed at high temperature. The results of chemical analysis reveled that the MBOA concentrations in leaf tissue decreased as the plants grew toward maturity, inversely the TLC plant ratings increased as the plants grew older. This showed that higher MBOA concentrations existed in the leaf tissue of earlier stage plants than in those of later ones. Leaf-feeding ratings after artificial infestation with Asia corn borer (ACB), Ostrinia furnacalis (Guenee) egg masses and number of surviving borer larvae per plant increased as the plants grew older, indicating that younger plants were more resistant than older ones to corn borer feeding. Of 11 inbred lines tested JT 30-1-1-1-15-3 and CI31A had lower leaf-feeding ratings, lower number of surviving larvae per plant and higher MBOA concentrations than any other lines at various stages of plant development. This implies there 2 lines possess a remarkable degree of resistance to leaf feeding by corn borer.
The correlation coefficients of MBOA concentrations with leaf-feeding ratings at the 4th, 6th, 8th, 10th and 12th leaf stages are as followings: -0.85, -0.84, -0.86, -0.82, and –0.84 respectively, meanwhile the correlation coefficients of MBOA concentrations with number of surviving larvae at the same leaf stages, in order, are as follows: -0.88, -0.83, -0.82, -0.78 and –0.80, respectively. The negative correlations of MBOA concentrations with leaf-feeding ratings and number of surviving borer larvae per plant were highly significant. This means the higher the MBOA concentrations in leaf tissue, the lower the leaf-feeding ratings and number of surviving borer larvae per plant. The results prove that DIMBOA is an important chemical factor in maize responsible for resistance to the ACB.
Key words: Corn leaf stage, DIMBOA, Asian corn borer, Insect resistance
Accepted for publication: April 16, 1996