Extremes of horizontal resistance

When the disease first appeared in East Africa, in 1952, at sea level, near the equator, the epidemiological competence was maximal, and the level of the horizontal resistance was minimal. Under these circumstances, the loss of crop was total, except for a handful of seed sufficient to plant the next crop. Some 10-15 maize generations later, the levels of both the epidemiological competence and the horizontal resistance were maximal, and the loss of crop was negligible.

Y-axis

Fig. 7.1 Epidemiological competence.

This diagram shows the extremes of epidemiological competence of Pucciniapolysora in East Africa. The level of epidemiological competence is measured on the Y-axis, with maximum at the top, and minimum at the bottom. Altitude is shown on the X-axis, with sea-level at the left, and 4000 feet at the right. Latitude is shown on the Z-axis, with the equator at the right, and the Tropics of Cancer (23.5°N) and Capricorn (23.5°S) on the left. The epidemiological competence is at its maximum at sea level on the equator. In this area, the local agro-ecotypes have the maximum level of horizontal resistance.

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