A week ago or so I saw some surprising pictures of 'Agnes' (H. Rugosa) bearing pink flowers rather than the usual light amber-yellow.
Patricia Routley explained that the flowers opened following a heat wave. She also noted that the flowers had fewer flowers than usual. That rang a bell for me.
https://www.helpmefind.com/rose/l.php?l ... &qn=1&qc=0
The expressions of some traits are greatly influenced by environmental conditions. In some cases that have been studied, low temps favor increased branching in the inflorescence, and more petals. Conversely, higher temps tend towards fewer flowers and petals. For example, Semeniuk (1962) reported that a seedling of 'Ma Perkins' bore flowers with only 5 petals when raised at 92 degrees F.
I don't want to run ahead of the evidence, but I can think of a few varieties that might be easier to use in breeding with fewer petals. 'Marechal Niel' is one example. Another, 'Rosette Delizy' is even further along the road to sterility. Then there is Rosa banksiae lutea. Could some heat applied at the right time nudges some of those petals to revert to stamens?
Semeniuk: Temperature and Rose fertility (1964)
http://bulbnrose.x10.mx/Roses/breeding/ ... p1964.html
Moe & Kristofferson: Temp & Light & Roses (1969)
http://bulbnrose.x10.mx/Roses/breeding/ ... t1969.html
Moe: Growth and Flowering in Roses (1988)
http://bulbnrose.x10.mx/Roses/breeding/ ... s1988.html
A meeting place for rose breeders.
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