Comparative N Response of Maize Cultivars Developed for Drought and Striga Resistance During Three Breeding Eras.

Breeding for resistance to Striga hermonthica (Del.) Benth and tolerance to drought has been a major strategy to improve maize (Zea mays L.) production and productivity in west and central Africa during the last three decades. The three decades of breeding for drought tolerant and/or Striga resistant early maturing maize started from 1988 and may be divided into three eras based on the germplasm and methodologies used. The eras are 1988-2000, 2001-2006 and 2007-2011. A total of 50 drought tolerant and/or Striga resistant cultivars were developed during this period, including 15, 16 and 19 cultivars for the three eras, respectively. Although the cultivars were not selected intentionally for low-N tolerance, it was hypothesized that tolerance to low N had been significantly improved while selecting for drought tolerance and Striga resistance. This hypothesis was tested by evaluating the 50 cultivars in 2010 and 2011 at Mokwa,, Nigeria a southern Guinea savanna location and Ile-Ife, a rainforest location under both low and high N levels. Under low-N conditions, grain yield (±standard error) improved from 2.28±0.056 t ha-1 during the first era to 2.61±0.054 t ha-1 during the third era, an increase of 0.165 t ha-1 per era with r2 of 0.99. Under high N, yield increased from 3.2±0.176 t ha-1 to 3.65±0.068 t ha-1, an increase of 0.225 t ha-1 and r2 of 0.93. Relative gain per era (that is, gain in grain yield in an era per unit yield in the previous era) was 0.03 t ha-1 per t ha-1 for the two N rates with r2 values of 0.99 and 0.94 respectively. Highest yielding cultivars under both N treatments were those developed during the third era. Increased grain yield was associated with significant delay in leaf senescence without significant changes in days to anthesis and silking, anthesis-silking interval, plant height or ears per plant. Grain-yield performance of the 50 cultivars under low-N conditions adequately predicted their performance under high N. We concluded that Striga and or drought tolerant maize cultivars are also low-N tolerant but low-N tolerant varieties are not necessarily Striga tolerant.