Mass Selection in Sweet Potato: Breeding for Resistance to Insects and Diseases and for Horticultural Characteristics1

Abstract

Advances attained by the sixth generation of mass selection in sweet potato (Ipomoea batatas (L.) Lam.) were assessed. The objective was to combine multiple resistances to pathogens, nematodes and insects with other desirable production and market qualities. Although progress from 6 single-year cycles of selection was encouraging, a change to 2-year cycles was indicated. Generation 6 contained high frequencies of flowering and seed set, attractive root shape, orange flesh, thin cortex, root specific gravities of about 1.02, acceptable yield, and resistance to fusarium wilt (Fusarium oxysporum f. sp. batatas (Wr.) Snyd. and Hans.), the southern root-knot nematode (Meloidogyne incognita (Kofoid and White) Chitwood) and the following soil insects: the southern potato wireworm (Conoderus falli Lane), the banded cucumber (Diabrotica balteata LeConte), the spotted cucumber beetle (D. undecimpuncta howardi Barber), the elongate flea beetle (Systena elongata (F.)), a white grub (Plectris aliena Chapin), and the sweet-potato flea beetle (Chaetocnema confinis Crotch).

Genetic Diversity of North American Strawberry Cultivars

“…Selection intensity should be relaxed in the first few generations while linkage groups are broken up (36,37). Development of commercially acceptable cultivars from this population will require more generations of selection than a backcross system of mating, but continued improvement of multiple traits derived from both the wild and cultivated species would be expected for many generations (43).…”

Control of Soil Insect Injury by Resistance in Sweet Potato

“…Thus, we consider the white grub control levels estimated here (Table 2) for 'Regal' and 'Southern Delite' to be realistic. Small roots are less vulnerable to soil insect injury than large roots because of a reduced surface area and because they are more likely to have escaped injury by early season insect populations (5,9,10). Thus, the low yields of the resistant control (W-13) were of some concern (Table 3).…”

“…Inheritance of resistance to soil insects proved to be independent of other desirable characteristics and, as a consequence, there did not appear to be a major barrier to development of insect-resistant cultivars equivalent in all other respects to those in commercial use (9). Selection for resistance to soil insects was given high priority in our breeding program (10,11). Subsequent tests (6,17) demonstrated the value of resistance as an adjunct or alternative to insecticides.…”

Heritabilities of Sweet Potato Resistances to Root Knot Caused by Meloidogyne incognita and M. javanica1

“…Each year we polycross 30 selections in replicated nurseries where all crossing is by naturally occurring insects. Selection of parental lines is based on a combination of factors associated with high yield, good root quality, and disease and insect re sistance (10). The parent lines used in the 3 tests reported here were from the 1975 and 1976 polycross nurseries and the offspring were their respective open-pollinated progeny (Tables 1 and 2).…”

“…in sweet potato has been recognized for many years (11,14,16). Cultivars and breeding lines are now routinely evaluated for reaction to this serious disease (10,13). Considerable variation occurs in field populations of M. incognita and culti vars are known to react differently to the various species and physiological races of root knot nematodes (2,6,7).…”