Preharvest Sprouting (Vivipary) in Pecan

1. Preharvest Sprouting (Vivipary) in Pecan Bruce W. Wood United States Department of Agriculture, Agricultural Research Service, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA 31008

2. Vivipary: Germinating, or producing seeds that germinate, before becoming detached from the parent plant Viviparous species are most commonly found in wet habitats, occurring in at least 78 families, 195 species and 143 genera (Farnsworth, 2000).

3. Vivipary The economic impact of vivipary in North America is usually most severe in the lower San Joaquin Valley of California, lower elevations in Arizona, portions of the mid to lower Rio Grande Valley of Texas, and lower elevation arid regions of northern Mexico (Brison, 1974; Zertuche, 1986; Ou et al., 1994); yet, it can also be an occasional problem for orchards at many other locations. It potentially occurs in most pecan cultivars if conditions are right.

4. Factors Affecting Vivipary • Vivipary incidence increases with increasing: • Crop-load (Finch and Van Horn, 1936; Stein, 1985; Zertuche, 1986; Sparks et al., 1995; Sparks, 2002; Sparks, 2005) • Length of growing season (Finch, 1933) • Time nuts are in trees or on the ground before harvesting • Vivipary is also influenced by: • Environmental factors such as: • Night temperature (A. Largua, unpublished data); closely associated with high temperatures during the latter stages of kernel filling (yet high temperatures alone do not necessarily lead to vivipary) • Irrigation (Stein, 1985), • Soil characteristics, light conditions, and blackmargined pecan aphid (Monellia caryella) populations (B. Wood and S. Sibbett, unpublished data). • Pollen source with the problem being reduced when fertilized by certain northern adapted genotypes (Ou et al., 1994) • Delayed shuck opening or splitting

5. Vivipary Orchard practices that can minimize vivipary: • Temik [Aldicarb; 2-methyl-2-(methylthio)-proprionaldehyde-0-(methylcarbamoyl)-oxime] to advance early-ripening • Avoiding excessive crop-load by either timely ‘mechanical thinning’ or by indirect fruit thinning via ‘hedge pruning’ • Early harvesting using mechanical shakers.

6. Experiment 1: Influence of irrigation and nitrogen fertilization on vivipary. Two-factor factorial [water (W) and nitrogen (N) at two levels (dry vs. wet; N vs. no N)]; 6 single-tree plots as RCB (n = 24); ‘Cheyenne’; heavy crop load. • Dry without N ( ‘-W-N)’ • Dry with N (‘-W+N’) • Wet without N (‘+W-N’) • Wet with N (‘+W+N’) ‘–W’ = no supplemental water during the growing season (i.e., residual soil moisture and rainfall only). ‘+W ‘ = drip-irrigation throughout the growing season at a rate of 23 L per hour for each of 8 h per day, and continuously over weekends. ‘–N’ = no supplemental N within one year preceding treatment or within the growing season. ‘+N ‘ = 59 kg N/tree [2 kg N (as ammonium nitrate) in mid April + 2 kg N at biweekly intervals from early July to late September].

7. Influence of water and nitrogen on incidence of vivipary Both irrigation and supplemental nitrogen fertilization increases incidence of vivipary

8. Vivipary: ‘Water x Nitrogen Interaction’ (P <0.0001) Fig. 1. Influence of supplemental drip irrigation (W) and supplemental N fertilization (N) on vivipary incidence of ‘Cheyenne’ pecan. -W = dry soil (not irrigated), +W = wet soil (drip irrigated), -N = low N (no N applied), +N = high N (multiple N applications). Treatment means with different letters are statistically significant by Tukey’s HSD test at a = 0.05.

9. Experiment 2: Role of abscisicacid (a plant hormone) in vivipary. • It is hypothesized that endogenous ABA, a plant hormone, within developing pecan kernels regulates vivipary. If true, incidence should be influenced by inhibitors of ABA anabolism or by supplemental ABA. • Treatments were: a) Untreated control b) Water:Ethanol (80:20; surfactant + foil) c) Fluridone (surfactant + foil) d) ABA (surfactant + foil) • Randomized complete block (RCB); 5 blocks, with single-tree experimental units (n = 25). • Approximately 100 individual fruit of terminal shoots were wrapped in cotton, sealed with aluminum foil, and the void injected with five ml of the treatment solutions of either water, fluridone, or ABA [in water:ethanol (80:20 v/v)]. • Fluridone (formulated as Sonar, Elanco Products, Indianapolis, IN) was applied at a solution concentration of 200 μg. ml-1; whereas (+)ABA was applied at a concentration of 300 μg.ml-1. • Treated fruit clusters were hand thinned to < 2 fruit per cluster. • The non-ionic surfactant was an organosilicone at 0.01% (Silwet L-77; Helena Chemical Co., Fresno, CA). • Fruit were retreated tri-weekly from early August until early October (liquid endosperm through kernel filling stages), for three applications per treatment. • Fruit of the three treatments were examined for external evidence of vivipary (i.e., split shell or emerging hypocotyl) after splitting of the shuck, but before dropping from the tree in late October. Incidence of vivipary was then determined by noting the proportion of viviparous fruit per treatment per replicate, and the data analyzed by ANOVA, with means separated by Tukey’s HSD test.

10. Fig. 3. Influence of fluridone, (+)ABA, and controls (non-treatment and treatment controls) on viviparous germination of ‘Oconee’ pecan fruit. Treatment means with different letters are statistically significant by Tukey’s HSD test at a = 0.05.

11. Experiment 3: Influence of fluridone on nut germination Fig. 2. Influence of fluridone and controls (non-treatment and treatment controls) on germination of ‘Sumner’ pecan nuts. Regression equations for germination percentage as a function of time in days (x) are as follows: Fluridone treatment is y = -4.21 + 0.01x + 0.0027x2 (R2 = 0.96, P <0.005); non-treatment control is y = 3.59 + 0.77x + 0.029x2 (R2 = 0.95, P <0.005); treatment control is y = 6.86 -1.10x + 0.035x2 (R2 = 0.99, P <0.005).

12. Conclusions • Water and nitrogen management strategies have the potential to influence crop loss to vivipary in commercial orchards. 2) High availability of water and N apparently interact to reduce bioactive ABA in developing fruit; thus, increasing vivipary. • ABA decreases and Fluridone increases incidence of vivipary; thus, vivipary appears to be strongly linked to ABA associated physiology of the developing fruit. • Because metabolic water is critical to embryo metabolism and development, its availability, and factors contributing to availability, favor vivipary. The combination of high NO3- , high seed moisture, warm night temperatures, and low ABA concentration or sensitivity, collectively appear to act as powerful triggers of vivipary. 3) It is postulated that crop loss to vivipary can be reduced by refinement of orchard management strategies to: • Protect nuts from supra-optimal late-season tissue N (most likely nitrate-N) concentrations and possibly excessive soil moisture (nitrate appears to modulate fruit metabolism) • Optimize micronutrients closely linked to the chemical reduction of inorganic N (NO3-), such as Fe, Cu, Mn, Zn, Ni.

13. Thanks!

14. Fluridone: An inhibitor of ABA anabolism Fluridone (Sonar or Brake) (1-methyl-3-phenyl)-5-3-(trifluoromethyl) phenyl-4(1H)-pyridinone) Abscisic Acid (2Z,4E)-5-[(1S)-1-hydroxy-2,6,6-trimethyl-4-oxocyclohex-2-en-1-yl]-3-methylpenta-2,4-dienoic acid