Sorghum tolerance to low-phosphorus soil conditions Willmar L. Leiser, University of Hohenheim, Germany; H. Frederick Weltzien-Rattunde and Eva Weltzien-Rattunde, University of Wisconsin-Madison, USA; and Bettina I.G. Haussmann, University of Hohenheim, Germany

1 Introduction

2 Phosphorus: a worldwide future challenge

3 Breeding sorghum for low-P soil conditions

4 Plant adaptation to low-P conditions

5 Summary: implications for applied sorghum breeding in West Africa

6 Future trends and challenges in bringing benefits of sorghum low-P tolerance to West African farmers

7 Where to look for further information

8 References

Phosphorus (P) is an essential plant nutrient. Phosphate rock, the main source of P fertilizer, is finite and just five countries control an estimated 88% of the global phosphate rock reserves. Many sorghum-growing areas in Africa are affected by P scarcity, and in these areas small-scale farmers depend on sorghum for food security and income but have difficulty accessing or paying for P fertilizer. With the expected future price increases for P fertilizer, the major but hidden P-deficiency problem will only worsen. Therefore, enhancing sorghum tolerance to low-P soil conditions is of great importance both now and for the future. This chapter first gives an overview of the worldwide P challenge, and then focuses on sorghum breeding for low soil P conditions, taking breeding for smallholder farmers in West Africa as a case study. The issues and challenges presented are:

• Breeding sorghum for smallholder farmers in West Africa; • Genotype selection under low-input conditions – challenges and solutions; • Quantitative genetics – a basis for setting up a specific breeding programme; • Adaptation of plants to low-P soil conditions; • Genetics of low-P adaptation.