The use of hybrids has made a significant impact on the productivity of maize throughout the world. The national maize program in Nepal has been active in maize research for more than three decades and has released numerous OPVs. Hybrid work, was initiated in 1987. During the initial stage commercial hybrids from neighbouring India were tested. More recent1y inbred and hybrids from CIMMYT have been utilized in developing a hybrid research program. A large number of hybrids that have potential for both the Terai and the hills of Nepal have been identified. This paper summarises the results of this early work. A hybrid variety is the first generation (F1) arising from a cross between two or more genetica1ly dissimilar genotypes (pure lines, inbreds, open pollinated varieties, populations etc.). Hybrid maize technology has evolved and passed through distinct stages over the past 100 years. A great deal of progress has been achieved in theoretical ideas and concepts related to various aspects of hybrid development but, more importantly, there has been significant impact from this technology which has dramatica1ly changed maize productivity in many regions of both the developed and developing world. Hybrid maize breeding that is practised today was started in the early 1900s with the work of Shu1l (1909) and East (1908). Shu1l (1908) determined that an open- pollinated maize cultivar includes an array of heterogeneous genotypes, which, upon inbreeding, would result in a series of pure lines (inbreds) which showed a loss of vigour. Hybrids of crosses between the pure lines regained the vigour (Shull, 1909). Based on his results Shull (1909,1910) postulated on what would later became the foundation of modem-day hybrid maize. Because of the low yields of inbreds and high cost of seed production of single crosses hybrid maize did not become popular initially until Jones (1918) suggested double cross combinations. Hybrid maize is produced in the industrialised world and hybrids are also grown increasingly in developing countries. Several studies have shown that at least 50- 63% of the yield gains in maize can be attributed to genetic improvement (Duvic,1992; Vasal et al.,1994).1n Asia, China, Thailand and Vietnam have made significant advances in hybrid maize technology (Vasal et. al.,1999 and currently have average yields of 4.9,3.2 and 2.4 t/ha, respectively (CIMMYT,l999).1n Thailand, 80% of the area is planted to single cross hybrids (Vasal et. al., 1999). CIMMYT initia1ly placed greater emphasis on developing open-po1linated varieties. However, after 1985 due to the increasing demand for hybrids in the developing world, it started to work on hybrids (CIMMYT,1993). This has led to the identification of several experimental hybrids and hybrid oriented germplasm which have shown superior yield performance as well as stability for yield across a range of environments (Srinivasan et al., 1993). This paper attempts to review the past research activities undertaken and efforts made towards developing hybrid maize in Nepal. Productivity gains from genetic improvement are probably the most cost-effective and ecologically sustainable gains. Of course, improved germplasm, be it open pollinated varieties or high-yielding hybrids, shows its full yield potential under high input conditions. Nevertheless even under low input conditions, improved cultivars have often been shown to yield better than local cultivars.

English

0211|AGRIS 0201|AL-Maize Program|R01PROCE

Juan Carlos Mendieta

CIMMYT Publications Collection