INHERITANCE AND COMBINING ABILITY STUDIES ON GRAIN YIELD AND RESISTANCE TO MAIZE WEEVIL (Sitophilus zeamais, MOTSCHULSKY) AMONG EXTRA EARLY QUALITY PROTEIN MAIZE INBRED LINES

ABSTRACT
The maize weevil is one of the most important storage pests of maize in Ghana and Africa as a whole. It causes damage from as low as 20% to as high as 100% in untreated varieties. Developing resistant varieties has been identified as an important and environmentally friendly aspect of the integrated pest management system. However, little is known about the genetic control of resistance to the maize weevil in Ghana. The main objective of this research was to understand the genetic control and heritability of resistance to the maize weevil. The specific objectives were to identify promising genotypes with resistance to the maize weevil. Five parents were crossed in a complete Diallel mating design to obtain 20 hybrids. The 25 genotypes were planted again with two local checks to obtain their seeds. The seeds obtained from these genotypes were subsequently used in the laboratory evaluation for the identification of resistance of the genotypes to the three regional collections of the maize weevils. The laboratory assessment identified parent TZEEQI 111 as the best parental line for resistance to the maize weevil. It exhibited highly significant and negative GCA effects for weevil progeny emergence, percentage weight loss, percentage grain damage and susceptibility index. It also exhibited a positive and significant GCA effect for Median development period. Hybrids TZEEQI 111 × TZEEQI 139, TZEEQI 111 × TZEEQI 12, TZEEQI 111 × TZEEQI 61 and TZEEQI 12 × TZEEQI 66 exhibited significant SCA effects. Heritability estimates revealed high narrow sense heritability for F1 weevil progeny emergence, percentage grain damage and susceptibility index. These results suggest the presence of additive and non-additive gene action in the control of resistance to the maize weevil. Parental lines TZEEQI 111, TZEEQI 139 and TZEEQI 66 performed very well and as such should be considered when forming base population to initiate breeding programs for resistance to maize weevils.


CHAPTER ONE
1.0 INTRODUCTION
Maize (Zea mays L.) is cultivated extensively worldwide (FAOSTAT, 2014) and the highest ranked cereal in terms of grain yield per hectare in the world (M’mboyi et al., 2010). Worldwide production of maize in 2014 amounted to 2,039,153,437 tonnes (FAOSTAT, 2014). The United States of America is the highest producer of maize in the world (FAOSTAT, 2014). The top ten maize producing countries in Africa are South Africa, Nigeria, Ethiopia, Tanzania, Malawi, Kenya, Zambia, Uganda, Ghana and Mozambique (FAOSTAT, 2014). In sub-Saharan Africa, maize is the most important and the most widely cultivated staple food, occupying an area which is in excess of 33 million hectares annually (Macauley, 2015). An estimated yield of less than 1.8 t/ha is realized on farmers’ fields in Africa as compared to the average worldwide yield of 5 t/ha (Macauley, 2015). Maize yield in Ghana on farmers’ fields is estimated at 1.7 t/ha (MoFA, 2011).

Maize has several uses for different people all over the world including human food, livestock feed, and its use in several industrial products (Zunjare et al., 2015). About 66% of the maize produced worldwide is used in the livestock industry for the feeding of livestock, 25% for human consumption and 9% for industrial purposes (Verheye, 2010). In developing countries, however, over 50% of the maize produced is consumed as food by humans. In sub-Saharan Africa, maize production is so important that low maize production is frequently linked with famine and scarcity of food (Oppong, 2013).

Maize comprises approximately 10% protein, 72% starch, and 4% fat, contributing 365 Kcal/100 g of energy (Ranum et al., 2014). Maize also provides most of the vitamin B’s but lacks vitamin B12 and vitamin C. It is also a good source of fibre. Maize is however lacking in two important amino acids, specifically tryptophan and lysine (Ngaboyisonga and Njoroge, 2014).

In Ghana, maize is the most important cereal (FAOSTAT, 2014). However, maize is produced predominantly by smallholder farmers in Ghana under rainfed conditions (Ragasa et al., 2013).

It is estimated that a greater part of the maize produced in West Africa yearly, is damaged in storage before reaching the consumer (Hell et al., 2000). It is also estimated that about $4 billion worth of maize grains is lost after harvest in sub-Saharan Africa each year (FAOSTAT, 2014). The greatest damage is caused by insects (Ukeh et al., 2012). Insects damage 15 to 50% of the total maize produced each year in developing countries (Suleiman et al., 2015).

The maize weevil (Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)) together with the Larger grain borer (Prostephanus truncatus Horn (Coleoptera: Bostrychidae)) are the most important storage pests of maize (Derera et al., 2014). Sitophilus zeamais infestation commences on-field and continues into storage (Demissie et al., 2008). The maize weevil is reported to cause damage to untreated storage maize from trace levels to as high as 80% grain damage when conditions are favourable (Tefera et al., 2010).

The problem of protein deficiency in maize was solved with the development of maize fortified with Lysine and Tryptophan. Quality Protein Maize was introduced into Ghana with the development of Obatanpa (Asiedu et al., 2001). Quality Protein Maize developed earlier had soft endosperm, chalky and dull kernel appearance and were susceptible to storage grain pests (Ignjatovic-Micic et al., 2011). This situation was alleviated with the successful development of quality protein maize that was genetically improved and possessed hard endosperm (Vivek et al., 2008).

The maize weevil is controlled predominantly by the use of synthetic insecticides. However, increased public awareness and concern for environmental safety and health considerations are gradually making the use of these chemicals unpopular (Kanyamasoro et al., 2012). Hence the need to find alternative methods of controlling these insects. The use of resistant varieties provides a safer, more practical and economic method of controlling the maize weevil than any other control technique (Abebe et al., 2009). A number of factors, whether present alone or in combination with other factors confer resistance to maize. Some of these factors include kernel hardiness, good husk cover, kernel size and texture, starchy amylose content, phenolic content etc. (Gudrups et al., 2001).

However, little is known about the genetic control of resistance to the maize weevil and the mode of inheritance and how easily the resistance can be transferred to the next generation. The lack of knowledge on the genetic control of resistance to the maize weevil is hampering further improvement of Quality Protein Maize. The main objective of this study therefore was to understand the genetic control and heritability of resistance to the maize weevil.


The specific objectives of the study were to:
I. estimate the general combining ability (GCA) and specific combining ability (SCA) of the parental lines and their hybrids respectively, for yield and resistance to maize weevil

II. estimate mid-parent and better parent heterosis for resistance to maize weevil III. estimate broad sense and narrow sense heritability of resistance to maize weevil

IV.       identify promising genotypes with resistance to maize weevil.

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Item Type: Ghanaian Postgraduate Material  |  Attribute: 91 pages  |  Chapters: 1-5
Format: MS Word  |  Price: GH50  |  Delivery: Within 30Mins.
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