Gibberellic acid (GA) increased bolting from 4.2 to 12.8% in fall-planted ‘Yellow Grano’ onion when applied 5 times at 500 ppm from 3/9 to 5/21. A single GA treatment 4/12 did not affect bolting. GA at 1000 ppm applied 11/1 and 12/9 had no effect on bolting or total seed yields of 3 short-day cultivars, but it limited seed yield per umbel. January 14 and February 21 treatments of 1000 ppm increased bolting percentage from 42 to about 60 and the February 21 treatment increased seed yield. Germination percentage of harvested seed was not affected by treatment. All GA treatments caused leaf growth from lateral buds.
Spring application of 2-chloroethyphosphonic acid (ethephon) at 500 and 1000 ppm, N-6 Benzyladenine (BA) at 100 ppm or succinic acid-2, 2-dimethylhydrazide (SADFI) at 5000 ppm did not affect bolting percentage.
Ethephon treatments inhibited internal scale browning of onions held in common storage for 3 months. October or Nov. ethephon treatments at 2500 ppm reduced bolting from 42 to 29%, and a dual ethephon application 10/8 and 11/1 resulted in only 11% bolting.
More than 4500 accessions of eight genera including Pyrus at the National Clonal Germplasm Repository, Corvallis, Ore., require testing for cold hardiness. Since pear xylem deep supercools (7), differential thermal analysis (DTA) would be a suitable test if large numbers of samples could be examined simultaneously. The object of this study was to produce a method of multichannel DTA for defining cold hardiness of pear accessions. Visual browning was also examined to confirm cold hardiness values.
The effects of root anaerobiosis on root respiration and leaf conductance (kl) were determined in solution culture experiments. Respiration of feeder roots (<2 mm diameter) in air (21% O2) of Pyrus betulaefolia Bunge, Pyrus calleryana Decne, Pyrus communis L. (‘Old Home’ × ‘Farmingdale 97’) and Cydonia oblonga Mill. ‘Provence BA 29’ was reduced by no more than 50% after 21 days of anaerobiosis. In contrast, root respiration of Prunus persica (L.) Batsch ‘Lovell’ was reduced by 80% with anaerobiosis, whereas that of Salix discolor Muhl. increased. Reductions in kl with anaerobiosis generally were more pronounced than reduction in root respiration when measured in air. Respiration rates of aerobically or anaerobically treated pear roots were inhibited by 25% to 50% when incubated in 0.5% O2 compared to rates in air. More work is required in order to delineate the relationship of root respiration and kl with anaerobiosis.