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  • Author or Editor: Daniel H. Diaz x
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Pecan has an irregular bud break under mild climate areas, difficulting pollination and reducing yields, particularly in seasons when chilling accumulation is low and when only 50% of buds open. Hydrogen cyanamide (H2C N2) at 1, 2, 4% alone or with mineral oil (MO) at 2, 4% were evaluated for their effect on lateral bud opening of `Wichita' pecans, spraying branches on january 25 or february 8. H2C N2 and its mixtures with MO advances bud break 25 and 18 days as compared to control on first and second date application respectively; by march 20th shoots on applied branches had 8-14 cm lenght while control and MO treatments had only 2-3 cm.

Initial bud break was up to 85% on treated branches as compared to 60% of control; however and regularly, some shoots emerging from buds abscise thereafter. Remaining shoot number per branch was 4.8 with 4% H2C N2 or the mixture 2% H2C N2 + 2% MO on the first application date, and with 4% H2C N2 + 2% MO on the second date, as compared to 2.5 shoots of control. A 12% bud injury occurred with 4% H2C N2 on first date application and high rates of mo of second date.

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Chilling accumulation infuence dormancy of grapevines and determines budbreak. Under desert conditions, hydrogen cyanamide (H2CN2) improve bud opening. To increase even further the quantity and uniformity of bud break, the effect of fall evap rative cooling (EC) alone or in combination with H2CN2(2.5%v/v was evaluated. Microsplinklers operated for 40 seconds at 10 min intervals from 10:00 h to 17:00 h, from 20 oct to 18 dec 1990. H2CN2 was applied on 21 dec, one day after pruning.

Cyanamide treated plants or with the chemical + EC, had 19% and 32% budbreak, respectively, by jan 15. Control or EC vines opened until feb 20, and reached 40% and 57% final values by mar 25. Therefore, cyanamide and EC acted sinergisti cally to open buds earlier and uniformily, although not on final budbreak.

Harvest started may 8 with cyanamide + EC, five days earlier than cyanamide alone; by may 13, accumulated harvest was 39% and 13% respectively, and of 92% and 77% by may 28. Control vines with or without EC, were harvested early may to mid june.

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An inhibitor was present in both seed coat and embryo of a high and a low chilling cv. of unstratified peach seeds and its concn decreased as stratification proceeded, Embryonic tissue retained more of the inhibitor than the seed coat. As the concn of inhibitor decreased, seed germination increased. The inhibitor was tentatively identified as abscisic acid (ABA) by chromatography. A bound inhibitor was also present in the seed parts of both cvs., and its concn increased in the embryo as stratification proceeded. More ABA and bound inhibitor were present in the high-chilling cv. than in the low-chilling counterpart, indicating that they may be related as factors which cause a cv. to require long periods of chilling. Application of ABA reduced germination percentage on stratified seeds without seed coats. Application of gibberellic acid (GA) and N-benzyladenine (BA) combined had a synergistic effect in promoting germination of dormant seeds.

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