j. Bolanos Defined drought resistance as capacity t yield without stress symptoms and tolerance as yielding capacity with symptoms. Studied 14 traits previously known to be associated with drought tolerance and found that ears per plant and shorter anthesis to silking (ASI) interval were most useful. ASI is manifestation of partitioning of dry matter to the ear. One day of ASI reduces maize yield by 10%. Drought stress increases the variance for barrenness, increasing a breeder's ability to identify genotypes that invest more in the ear.|Y. Chantachume Discussed the importance of breeding of stress tolerance in light of the rising cost of inputs, especially N fertilizers, in South East Asia. Studied inbred lines under low and high N levels and found that ears per plant and ear aspect were closely associated with N use efficiency. Yield under low and high N had a phenotypic correlation of 0.71, which lead him to conclude that only one level of N was sufficient to select for N efficient maize genotypes. For drought, he found that wilt score and plant recovery were traits that showed a correlation of about 0.50 with yield under this stress.|N.N. Singh About 3 million ha of maize area in Asia was under water-logging (WL), nearly 2.5 million ha in India alone. Late maturity materials suffer twice as much yield reduction under WL (50% ) as do the medium and early maturity germplasms (25% ). ASI is correlated with yielding ability under WL. Adventitious roots help reduce WL losses. One white and one yellow endosperm pools have been developed and improved for seven cycles under WL treatments applied for three days at seedling and pre-flowering stages. WL at seedling stage is most critical. Lines, hybrids, and synthetics will be developed and several basic studies are planned.|C. de Leon Nearly 60% of agricultural land in acidic. In such soils, All toxicity and P deficiency are prevalent. Four populations have been developed, two white and two yellow endosperm. Populations within one color are heterotic and . are being improved using reciprocal recurrent selection. Additive and non-additive genetic variances provide tolerance and narrow sense heritability averages about 36%. Dominance x environment interactions are insignificant, suggesting that stress tolerant hybrids can be developed more efficiently. Superior single crosses yield about 50% more (6- 7 tons) than superior OPVs under stress but tolerant materials yield well under both stress and nonstress conditions.|S. Vasal Suggested integrating disciplines and scientists to develop stress tolerant germplasm more efficiently. Maize is a plant with "a crop of options" and stress breeding "is a big puzzle". Drought, low N, high density, inbreeding, etc., all contribute to stress. Stress breeding is complex in both genetic and environmental manipulations. Germplasm with high mean and adequate genetic variances are ideal for stress breeding. Suitable screening techniques are a necessity. Most breeding procedures work but suggested we use the ones more appropriate for the level of heritability for the trait. Selection for stress tolerance can be easily integrated in an on-going breeding program and must be an integral part of any maize research program. Traits that generally contribute to stress tolerance include yield, ASI, ear aspect, and ears per plant. Lines tolerant to most stresses are available from CIMMYT, in every maturity group.

English

0208|AGRIS 0201|AL-Maize Program|R01PROCE

Juan Carlos Mendieta

CIMMYT Staff Publications Collection