Ruiru 11, a hybrid of Catimor and SL cultivars, is both Coffee Berry Disease (CBD) and Coffee Leaf Rust (CLR) resistant. Plus, it can be planted at a much higher density than the SL varieties, making optimal use of small plots of land.
Ruiru 11 has slowly ‘taken root’ across most of Kenya’s coffee growing landscape. The only issues were that with a shallower root structure, many farmers found the plant less hardy in drought conditions, and the trees required a more intense feeding program. Over time, farmers have found that by grafting Ruiru-11 to SL varieties they could take advantage of SL trees’ expansive root system and still reap the increased yields and higher immunity to disease of Ruiru-11.
Due to the grafted Ruiru-11’s growing popularity, most farms in Kenya today, both big and small, have a mixture of Ruiru-11 and SL varieties. As SL trees age, many farmers are opting to turn more towards Ruiru-11 (or the grafting solution) thanks to its ease of use and higher resistance to diseases.
Source: https://varieties.worldcoffeeresearch.org/varieties/ruiru-11 & https://sucafina.com/na/news/think-you-know-kenya-coffee-varieties-think-again