A hibridação interespecífica no melhoramento do cafeeiro

Abstract

The cultivation of coffee in the American coffee producing countries is not faced with any serious handicap. The future can not be far distant, however, when it will be necessary to establish new plantations back on the high-priced old exploited lands. Need will be felt for improved varieties. At the same time, it is not known if in a near future the American coffee growers will not be in trouble with diseases as terrible as Hemileia, which the present age of transport cannot restrict to non-American areas. In the program of coffee improvement, interspecific crosses are expected to take a very important place. The introducing of desired characteristics of other species into Coffea arabica by hybridization is made difficult by the fact that, while C. arabica is self-fertile, the other species are self-sterile. It is known, also, that the high cup quality C. arabica species, with 44 somatic chromosomes, gives sterile triploid hybrids (2n = 33) when crossed to the leaf disease resistant Coffea canephora and other diploid (2n = 22) species. Very seldom, however, do the triploids produce seed, as a result of back-cross to C. arabica either through open or controlled pollination. The cytological constitution of the plants obtained from these seeds is variable ; some triploids give rise to seedlings having mostly a chromosome number around 44 ; the progeny plants from other hybrids have this number mostly around 55. Numerous aneuploids have been found among these progenies. Attention has been given to the plants derived from the hybrids as to their developmental and production characteristics. At least two 44-chromosome plants have shown to be interesting in these respects and one of them, productive and self-fertile, showed up characteristics very similar to the maragogipe variety of C. arabica. More detailed comparative observations are necessary ; however, the obtaining of such a plant proves that the triploids are a permanent source of new cytological combinations that can be used in the future in the search for new vigourous and disease resistant coffee plants with high cup quality.