The use of Rosa wichurana in the development of landscape roses adapted to hot humid climates
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The Robert E. Basye Rose Breeding and Genetics program is located in the southern zone of the United States where the warm humid climate favors the development of powDery mildew in the spring time (March through April) and black spot towards the end ofsummer and into the fall months. Furthermore, evergreen rose types are adapted to this region due to the relatively mild winters. Rosa wichuranaCrp. is a rose species that originated in China unDer mild winter conditions, though it is consiDered hardy to USDA Hardiness Zone 6. Thus, it is a potential parent for the development of good disease resistant roses that maintain foliage throughout the winter months. This species crosses well with a range of other species such asR chinensis Jacq., R roxburghii, R rugosa Thunb. and R xanthinaLindl. Of these hybrids, the hybrid plants with R rugosa and R xanthina were not fertile whereas the hybrid plants withR. roxburghii and R. chinensis had good fertility. The most useful hybrids were those between R wichuranaand R chinensis'Old Blush'. Although the initial hybrids were all once blooming, everblooming selections were developed by looking through large F 2 populations and by backcrossing to 'Old Blush'. These plants ranged in growth habits from ground cover to upright and had stems that had no prickles to dense prickles. The flowers ranged in petal number (single to double), flower color (white to dark pink) and flower size. These evergreen plants also varied markedly in the level of resistanceto both powDery mildew and black spot. The best recurrent bloomers without prickles have been crossed with commercial germplasm with a range of flower forms and color. The resultant seedlings are showing a wiDer range of flower forms and color and poor to good disease resistance.
