Breeding Peach For Narrow Leaf Width

Mature peach leaves are typically about 4 x 16 cm, with a width/length ratio of about 25%. A narrow leaf seedling, selected by Wayne Sherman (Univ. of Florida, Gainesville), was hybridized at USDA-Byron with adapted commercial varieties. Early generation hybrids produced small, irregular-shaped fruit. After 5 generations, current selections are approaching commercial fruit standards in size, color, firmness, and attractiveness. Narrow-leaf trees are often noticeably more open than standard trees. This leaf type may be useful in standardor high-density plantings to enhance spray penetration, to speed drying of wet foliage to reduce disease, to improve light penetration and photosynthetic efficiency for greater fruit size and red color, and to make the fruit more visible to speed picking. Inheritance studies indicate that the narrow-leaf character is at least partially dominant and is expressed in some F1 seedlings of crosses with wild-type parents. The exact inheritance remains unclear as the ratios obtained to date do not fit common inheritance patterns. Progeny vary in leaf width with ratios of width/length generally ranging from 10-25%. The most extreme seedling has leaves up to 28 cm long and 1 cm wide, and although it is not fruitful, it may have ornamental value. INTRODUCTION Peach (Prunus persica) leaves vary in width depending on age, shoot vigor and location within the canopy. Typical mature leaves on commercial varieties are about 4 x 16 cm, or slightly larger on vigorous shoots. Although leaves on a shoot will vary in length, the width varies proportionately so that the ratio is relatively constant regardless of the length (Fig. 1). On a seedling tree leaves are generally narrower for the first several growing seasons while the tree is in a juvenile stage. Narrow or narrow-leaf peaches (Fig. 2), characterized by a smaller leaf width/length ratio, were mentioned as far back as 1887 (Hedrick, 1917). Blake and Edgerton (1946) classified leaf width of standard leaves (1518 cm long) as medium if the width/length ratio was 2530%, as for ‘Elberta’. Ratios for 32 commercial varieties released from the New Jersey breeding program ranged from 22.2-27.5%. A ratio of 20-25% was classed as narrow, and less than 20%, very narrow. The only example of the latter class given was 'Sleeper', with a ratio of 18.6%. ‘Sleeper’ may be the same as ‘Sleeper Dwarf’ (Hedrick, 1917), in which case it may have had the abnormally long leaves typical of brachytic dwarfs, hence the low ratio. Narrow-leaf types were also noted by Lesley (1957) as a product of inbreeding. The narrow-leaf tree is noticeably more open than a standard tree. Despite the tree having a somewhat weak appearance, this character may be useful in standard or highdensity plantings to enhance spray penetration, speed drying of wet foliage to reduce disease, improve light penetration and photosynthetic efficiency for greater size and red color, and to make the fruit more visible, to speed picking. Narrow leaves have been shown to have a higher water use efficiency than standard leaves (Glenn et al., 2000). MATERIALS AND METHODS Around 1980 Wayne Sherman (University of Florida, Gainesville) selected a peach seedling with unusually narrow leaves from a group of seedling rootstocks. This