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

18, 10 and 5%, respectively. At present, no effective chemical is available for curing infected
plants. The most effective and economic method of protecting corn crops is to breed a hybrid
resistant to MDMV. However, selecting for MDMV resistant inbreds is essential in breeding
resistant hybrids. The MDMV resistant inbreds can be selected by the abrasion method, as
follows:
1.
2.
3.
4.
5.
6.
7.
Leaves infected with MDMV are collected from the susceptible variety Tainan No.5,
which is grown in a greenhouse as a source of inoculum.
The leaves are sliced into pieces. One g sliced leaves are ground with 10cc 6N Na 3
S03 solution and the juice is collected.
The juice is filtered through a piece of gauze and placed in a beaker.
The filtrate is neutralized to pH 7.0 by adding 6N H 2
S0 4
solution.
Cotton balls are soaked in the filtrate, and placed in 400 mesh carborundum.
The plants are artificially inoculated when they are at the 5th-6th leaf stage, by
rubbing the middle leaves with the cotton balls.
Two weeks after inoc~lation germplasm is rated as highly resistant (0-20% infection),
resistant (21-40%), having intermediate resistance (41-60%) or susceptible (61-100%),
according to the percentage of infected plants.
3. SCreening for resistance to stalk rot (P. aphanidermatl.l1l).
Stalk rot (P. aphanidermanum) can attack corn plants at any stage of development. The
disease can easily become destructive when temperature and humidity remain high, (i.e. over 27 0 C
and B6%, respectively) for 15-20 days (Dreschler, 1934). There is significant variation in
resistance to stalk rot in different germplasm. Disease resistant germplasm can be identified by
artificially inoculating corn plants at the second internode above the ground level when they
reach the 5th-6th leaf stage. The inoculum used for infection is cultured in media made up of
200 ml V-B juice, 10g caCo 3
, 20g agar, and BOO ml distilled water. Two weeks after inoculation,
germplasm is rated as highly resistant (0-20% infection), resistant (21-40%), intermediate
resistant (41-50%), and susceptible (51-100%), based on the percentage of infected plants.
4. SCreening for resistance to the Asian corn borer (0. furnaca7is).
It is impossible to evaluate germplasm for resistance to the Asian corn borer unless an
artificial diet is available for the mass production of corn borer egg masses (Awadallah, 1983;
Guthrie et al, 1965, 1970, 1987; Tseng, 1986). Asian corn borer can be mass produced in the
laboratory using an agar-based meridic diet. The ingredients used in the diet are listed in
Table 1.
Table 1.
Ingredients used in meridic diet for the Asian corn borer.
Ingredient Quantity Ingredient Quanti ty
Water 2340.0 ml Ascorbic acid 21.6 9
Agar 50.4 g Methyl p-hydroxybenzoate 3.0 9
Wheat bran 98.0 9 Sorbic acid 3.0 9
Dextrose 72.0 9 Aureomycin 625.0 mg
Casein 79.2 9 Propionic acid 12.0 ml
Cholesterol 5.8 g' Formaldehyde 1.0 ml
Wesson's salt 26.0 9 Streptomycin 110.0 mg
Vitamin complex 16.6 9
Wesson's salt (g) = NaC1: 105.00 g; KC1: 120.00 g; KH 2
P0 4
: 310.0 g; Ca 3 (P0 4
)2: 149.00 g;
CaC0 3 : 210.00 g; MgS0 4 7H 2 0; 90.00 g; FeP0 4 ,4H 2 0: 14.7 g; MnS0 4 : 0.20 g; K 2 A1 2 (S04224H20: 0.09
119