Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom.|Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Department of Statistics and Applied Probability, National University of Singapore, Singapore, Program in Health Services and Systems Research, Duke-NUS Graduate Medical School Singapore, Singapore, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore.|Department of Actuarial Mathematics and Statistics and the Maxwell Institute for Mathematical Sciences, Heriot-Watt University, Edinburgh, United Kingdom.|U.S. Dept. of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America.|Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom.