Genetic Improvement in Resistance to Striga in Tropical Maize Hybrids

Abstract

RESEARCHM aize (Zea mays L.) and other cereals like sorghum [Sorghum bicolor (L.) Moench] and pearl millet [Pennisetum glaucum (L.) R. Br.] are the major staple food crops for millions of people in sub-Saharan Africa. Striga hermonthica (Del.) Benth has been recognized as one of the most destructive parasitic weeds, with its haustorial cells penetrating roots of maize and the other cereals to derive the resources for its growth and development (Parker and Riches, 1993). Since the 1980s, maize production in West and Central Africa has expanded considerably into the savannas, which are high-production zones, where this endemic obligate root hemiparasite poses a serious threat to maize cultivation (Ejeta, 2007). The area infested with S. hermonthica and its negative impact continue to increase because of diverse parasite seed dispersal mechanisms, including contaminated crop seeds, animals, farm implements, wind, and surface water (Berner et al., 1995;Ejeta, 2007). Climate change may further increase the geographic distribution and invasive potential of S. hermonthica, as habitats suitable for its growth might expand (Mohamed et al., 2007). Growth and yields of maize are adversely affected by the withdrawal of water, nutrients, and assimilates by this root parasite from the host to sustain its development (Gurney et al., 1999), causing yield losses that can reportedly reach up to 100% in severely infested smallholder farmer fields in Africa (Kim et al., 2002;Ejeta, 2007).Many control methods, including hand pulling, crop rotation, trap and catch crops, and the use of herbicides and N fertilizer,

Gains in Genetic Enhancement of Early Maturing Maize Hybrids Developed during Three Breeding Periods under Striga-Infested and Striga-Free Environments

“…The 4.82% yield gain per year with an increase of 101 kg ha −1 in Striga-infested environments across the three breeding periods obtained in this study was considerably higher than the 3.28, 2.56, and 2.25% reported for a set of extra-early maturing OPVs under moisture deficit, Striga-infested, and optimal conditions, respectively [21]. Furthermore, the yield gain per year realized in the present study is also higher than the 1.93 and 1.0% reported for early maturing OPVs under Striga infestation and non-infested environments by Badu-Apraku et al [2] and 3.2% yield gain per year in Striga-infested environments reported by Menkir and Meseka [18] for intermediate maturing hybrids. The implications of these results are that early maturing hybrids responded better to selection for improved resistance to Striga, as well as high grain yield relative to the extra-early and early varieties as well as intermediate hybrids.…”

“…Yield gains of 0.86, 2.07, and 2.11% were reported for periods 1, 2 and 3, respectively. Also, in a genetic gain study involving 32 late/intermediate maize hybrids, Menkir and Meseka [18] reported an annual yield gain of 3.2 and <1%, which corresponded to an annual gain of 93.7 and 29.3 kg ha −1 under Striga-infested and non-infested environments, respectively. However, information is unavailable on how genetic improvement for Striga resistance has affected agronomic characteristics of early maturing maize hybrids, including grain yield.…”

“…Periodic assessment of genetic gains realized over time in a breeding program is helpful for evaluating the effectiveness of breeding methodologies and devising new strategies. Several studies comparing yield performance of maize varieties generated during different breeding periods have been carried out to document yield gain from selection [15][16][17][18]. Badu-Apraku et al [2] studied the yield gains of early maturing open-pollinated maize varieties (OPVs) of three breeding periods under Striga-infested and non-infested environments from 2010 to 2011.…”

Genetic Diversity and Population Structure of Maize Inbred Lines with Varying Levels of Resistance to Striga Hermonthica Using Agronomic Trait-Based and SNP Markers

“…Analysis of variance under Striga infestation showed that there was significant variation among the inbred lines used in this study. The significant difference observed across environments and genotype X environment interaction for most of the traits measured could be due to seasonal factors [ 54 , 55 ]. The hierarchical cluster analysis based on agronomic characteristics under Striga infestation grouped the inbred lines according to their reaction pattern to S. hermonthica, with most of the inbred lines in each group emanating from different source populations.…”

Effects of Maize (Zea Mays L.) Hybrids and Nitrogen Application on Striga Infection and Grain Yield under Natural Infestation with the Parasitic Weed Striga Hermonthica

“…These include the use of Striga-tolerant or resistant maize cultivars [18][19][20], application of nitrogen particularly for poor soils [8,14,21,22), legume-maize rotation [23][24][25][26], herbicide seed coating [21,27]. Maize breeders at the International Institute of Tropical Agriculture (IITA) have considered breeding for polygenic resistance to S. hermonthica as a viable approach to provide durable protection to the crop against diverse parasite populations [19]. As a result, significant increases in grain yield, coupled with reductions in parasite-induced damage symptoms, and number of emerged parasites have been reported [19,28,29].…”