traits may appear as separate, this does not mean that they are controlled by separate genes. For instance, pawpaw fruit size and seed size are highly correlated traits that are probably controlled by many of the same genes. If this is the case, then the breeding value formula should not use fruit size and seed size as directly measured, but should instead use two new variables that represent 1) the linkage of fruit size and seed size, and 2) the independence of seed size from fruit size.
The final selection of advanced numbered selections was not a purely mechanical exercise. Subjective judgments about tree worth entered the decision. And a conscious bias was exercised to select high ranking trees from different maternal lineages. After Peterson had identified a set of advanced selections a testing phase began that lasted about 6 years. Some selections were not stable when grafted unto other rootstock (e.g., PPF 2-54 and PPF 9-58). To eliminate the element of chance, testing included six to ten replicates.
THE PROSPECTS FOR PAWPAW BREEDING. The task of pawpaw breeding is now in the hands of amateur scientists with little institutional backing; KSU is an exception. The present pawpaw industry is too small to fund university breeding programs. Thus breeding is likely up to the amateur.
Recurrent mass selection, when performed with an intelligent eye for the selection of complementary high-quality parents, is a traditional method of plant breeding that can produce steady progress and does not require sophisticated equipment. First, hundreds or preferably thousands of seedlings must be grown to increase the chances of finding the truly superior genotype. Second, more traits in the selection index slow the rate of progress. Third, the pawpaw is an obligate outcrosser and is theoretically prone to inbreeding depression, a decline in yield and vigor. Therefore, a diversity of breeding lines should be maintained and outcrossed every few generations.
The amateur breeder must be dedicated to the task and willing to learn. Breeders should join groups like the NNGA and the PawPaw Foundation, and familiarize themselves with pawpaw history, biology, genetic resources and pollination techniques (e.g., Callaway, 1990; Jones et al., 1998; Peterson, 1991, 1997; Thomson, 1974). They should read books and articles about plant breeding, such as Callaway and Callaway (2000), Moore and Janick (1983), and Sparks (1992). Pawpaw breeding is long-term research requiring roughly 10 years per generation and 6 years for testing. However, neither extravagant budgets nor extensive acreage are required. Two or three acres will suffice. Persistence, a love of pawpaws, a logical mind, attention to detail, habits of close observation, and familiarity with the scientific method are required. Zimmerman began breeding pawpaws late in life and died before his most promising crosses bore fruit, and those crosses were subsequently lost to posterity. We do not wish to repeat that experience.
should read books and articles about plant breeding, such as Callaway and Callaway (2000), Moore and Janick (1983), and Sparks (1992). Pawpaw breeding is long-term research requiring roughly 10 years per generation and 6 years for testing. However, neither extravagant budgets nor extensive acreage are required. Two or three acres will suffice. Persistence, a love of pawpaws, a logical mind, attention to detail, habits of close observation, and familiarity with the scientific method are required. Zimmerman began breeding pawpaws late in life and died before his most promising crosses bore fruit, and those crosses were subsequently lost to posterity. We do not wish to repeat that experience.
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