Proceedings of the Fifth Asian Regional Maize Workshop - Search ...

g; CUS0 4 (5H 2 0): 0.39 g; NaF: 0.57 g; KI: 0.05 g.
Vitamin complex (g) =Vitamin A: 2.70 g; Vitamin D: 0.15 g; Vitamin E: 3.00 g; Vitamin C:
27.00 g; Inositol: 3.00 g; Choline Chloride: 45.00 g; Riboflavin: 0.60 g; Menadione: 1.55 g; P­
Aminobenzoic acid: 3.00 g; Niacin: 2.70 g; Pyridoxine hydrochloride: 0.60 g; Thiamine hydrochloride:
0.60 g; Calcium pantothenate: 1.80 g; Biotin: 0.012 g; Folic acid: 0.054 g; B 12 : 0.0018 g;
Dextrose: 512.45 g.
In Southern Taiwan, there are usually six to eight generations of the Asian corn borer per
year, with a population increase from late March until the end of OCtober. Resistance in hybrid
corn to the Asian corn borer should therefore be sustained through all stages of plant development.
Resistance at the whorl and pollen-shedding stages is conditioned by different factors.
High concentrations of DIMBOA [2, 4-dihydroxy-7-methoxy-(2H)-1, 4 benzoxazin-3 (4H)-one] have
been proved to have a closer relationship with resistance to the Asian corn borer at the whorl
stage than at the pollen-shedding stage (Klun and Robertson, 1969; Tseng, 1989). Thus, evaluation
of corn germplasm resistant to the Asian corn borer at the whorl and pollen-shedding stages
should be conducted separately, then the resistant factors at both stages combined in a single
plant by breeding (Penny et a7, 1967).
To screen germplasm resistant to the Asian corn borer at the whorl stage, egg masses are
dropped into the plant whorls (30-35 days after germination. Satisfactory levels of infestation
can be obtained by three applications (60 eggs per application) spaced two or three days apart.
A 1-9 class rating scale was used to evaluate the amount of plant injury in corn for different
levels of larval establishment and survival (Guthrie, 1960).
Class 1. No visible leaf injury, or a small amount of pin or fine shot-hole type of
injury on a few leaves.
Class 2. small number of shot-hole type lesions on a few leaves.
Class 3. Shot-hole injury common on several leaves.
Class 4. Several leaves with shot-hole and elongated lesions.
Class 5. Several leaves with elongated lesions.
Class 6. Several leaves with elongated lesions (2.5 cm).
Class 7. Long lesions common on about one half of the leaves.
Class 8. Long lesions common on about two thirds of the leaves.
Class 9. Most leaves have long lesions.
Genotypes created 1 and 2 are considered highly resistant, 3 and 4 reSistant, 5 and 6
intermediate in resistance, and genotypes that rate 7 to 9 are considered susceptible.
To evaluate the resistance of corn plants to the Asian corn borer at the pollen-shedding
stage, egg masses incubated until they are near hatching are pinned to the midrib of the leaves
above and below the ear during anthesis. Fifty to sixty days after the first infestation, the
number and size of cavities inside the stalk are counted. A cavity 2.5 cm long is counted as one
cavity, a cavity 15 cm long is counted as six cavities and so on. The corn genotypes are then
classified into highly resistant (0-20 cavities), resistant (21-40 caVities), intermediate
resistance (41-60 cavities), and susceptible (over 61 cavities).
5. Strategies to breed hybrid corn varieties which are high-yielding, resistant to pests and
lodging, and tolerant to high soil moisture.
1. Development of the basic population (CO).
For creating potential genetic variability in the CO population for a long-term breeding
program, the parents selected to be recombined into one population should have superior resistance
to stalk rot, MDMV, downy mildew, and the Asian corn borer (Klenke, et a7, 1986; Davis &
Crane, 1976). For the most favorable alleles to be present in a single segregate, the hybridization
method of convergent crossing with modified backcrossing (Gallum, 1979) is used to form the
CO population (Fig. 1).
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