Posts Tagged: alternate bearing

Avocados, Flowers, Bees, Pollination and Fruit. That Simple?

Avocado trees can appear completely covered with flowers. A typical full grown healthy avocado tree in California can produce up to a million flowers a year, but, on the average, fewer than 200 flowers per tree will set fruit that will hold and develop to maturity and harvest (about 10,000 lbs/acre, or less). Upon occasion, we have seen some groves with trees setting an average of 500 flowers per tree (25,000 lbs/acre), but this is rare. More commonly, only 100 flowers (or less) per tree will set and hold fruit to maturity (5,000 lbs/acre or less), much to the distress of growers (Bender 2013).  Flowering is typically spread over six to eight weeks.

The avocado flower has both functional male and female organs. The male floral organ, which produces pollen, is comprised of the anthers and stamens. The female floral organ is comprised of the stigma (which receives the pollen), style and the ovary. The flowers are small (10 mm diameter). The flowers are usually only open for 2–6 hours, then close and open again for 2–6 hours on the second day. When a flower opens for a second time, it produces pollen and the stigma is not receptive. Flowers then close and remain closed. Flowers will usually be one sex in the morning, closed in the middle of the day and the opposite sex in the afternoon. The timing of the sex phases can be quite defined, but environmental conditions will affect the timing and duration of the male and female phases. The mature tree can produce in excess of a million flowers during the flowering period. 

Avocado cultivars are classified in two groups (A or B) based upon their flowering behavior. In the type ‘A' cultivars, the female organs are receptive to pollen in the morning and the pollen is released in the afternoon. Unfortunately, most of the currently available "B" varieties are classed as "greenskins", which return less to growers. In the type B'cultivars, the pollen is released in the morning, while the female organs are receptive in the afternoon. Type A cultivars include: Hass, Gwen, Lamb Hass, Pinkerton, Reed, Gem, and Harvest.  Type B cultivars include: Bacon, Ettinger, Fuerte, Sharwill, Sir Prize, Walter Hole, Zutano, Marvel and Nobel. Both type. It is believed that the interplanting of complementary flower types can boost fruit set and therefore yield by making pollen available. The separation in time of the male and female phases has led most observers to believe that a vector or "pollinator" is needed to move pollen from one flower to another.

Steps to take to Improve Pollination (Bender 2014):

 1. Bring beehives into the grove. The University of California farm advisors have usually recommended 1 – 2 strong hives per acre, but Ish-Am (2000) suggests that 1 hive is rarely sufficient, and in many cases 4 hives are required. California growers usually have to rent hives (in 2002 hive rentals averaged $42 per hive), but sometimes beekeepers will drop a load of 80 hives for free if the grower has good bee forage nearby. Bees should have water available; floating boards on ponds or reservoirs enables them to land and drink without drowning.

 

2. Add pollinizers to the grove. Ish-Am recommends a pollinizer tree row be located at least every fourth row. Some growers in California use pollinizers as wind-breaks around the grove, and some replace thinned-out trees with pollinizers.

 

3. Keep the orchard open. Direct sunlight should reach the lower branches of each tree in order for the trees to produce a “wall” of flowers down the ground. In avocado production, this can only be accomplished by pruning the upper branches on a yearly basis. Keeping open channels through the grove encourages the flight of bees.

 

4. Other types of bees? Bumblebees have been reported to increase yield in avocados in Israel where honeybee populations were low. New World Carniolan bees have been used in an experiment in San Diego County for pollination: results were inconclusive as to whether they increased yield compared to Italian honeybees, but it was found that they gather more nectar from avocado (Fetscher et al. 2000). Work with these bees, and other wild bees, may eventually reveal a more efficient pollinator for avocado.

 

Citrus Grower Meeting Coming Soon

Every year growers get together to learn what is being done in the citrus research world that could affect their operations. This June, University of California and the Citrus Research Board are bringing some good talks to three different growing areas. All growers are invited, but RSVPs are appreciated.

 

CRB-GrowerSeminar-Flyer 2017

PGRs aand Olives

Advances in mitigation of alternate bearing of olive: vegetative growth response to plant growth regulators

Elizabeth Fichtner, UCCE Farm Advisor, Tulare County, and Carol Lovatt, Professor of Plant Physiology, Botany and Plant Sciences, UC-Riverside.

Alternate bearing (AB) is a phenomenon in olive where fruit production alternates between large crops consisting of smaller, lower value fruit during an ‘"ON’ year and smaller crops consisting of larger, higher value fruit during an "OFF" year. The large swings in biennial olive production impact the overall industry, from growers to harvesters, to processors. In olive, the vegetative growth in one year produces the nodes bearing potential floral buds in the spring of the second year. Fruit suppress vegetative shoot growth resulting in fewer nodes available to bear fruit the following year. Our phenological studies have helped characterize the relationship between fruit load and vegetative growth on ‘Manzanillo’ olives in Tulare County, California.

Investigation of vegetative growth response to plant growth regulators

One strategy proposed to mitigate AB is to stimulate summer vegetative shoot growth to increase the number of nodes with the potential to produce floral buds. To address this strategy, our research team designed and implemented a proof-of-concept study in which plant growth regulator (PGR) treatments were injected into individual scaffold branches on opposing sides of ’ON‘ and ’OFF‘ trees. Plant growth regulators utilized in the study included two cytokinins, 6-benzyladenine (6BA) and a proprietary cytokinin (PCK), as well as two auxin-transport inhibitors, tri-iodobenzoic acid (TIBA) and a natural auxin transport inhibitor (NATI). Eight PGR treatments were included, with each PGR tested alone, and each cytokinin tested in combination with each auxin-transport inhibitor. PGR treatments were implemented in Summer (July 2012), and Summer + Spring (July 2012 and February 2013). Vegetative shoot growth was recorded monthly throughout the year to determine the influence of PGR treatments and timings on node production. The study was completed at the Lindcove Research and Extension Center (Exeter, CA).

Node production in response to plant growth regulator treatments

Scaffold injection with numerous PGR treatments resulted in significant increase in vegetative shoot growth. For example, nonbearing shoots on ‘ON’ control trees, produced an average of one node between July 2012 and February 2013, whereas nonbearing shoots on   PGR-treated scaffold branches exhibited almost 4 times the new growth of the control trees (Table 1, shaded). Importantly, the new growth in some cases was statistically equal to and numerically greater than the new vegetative shoot growth of nonbearing shoots on ‘OFF’ control trees. The PGR treatments also had a positive effect in increasing vegetative shoot growth on bearing shoots of ‘ON’ crop trees. Bearing shoots on ‘ON’ control trees produced an average of 0.8 nodes between July 2012 and February 2013, whereas bearing shoots on PGR-treated scaffold branches of ‘ON’ trees produced over three-fold more nodes during this period. Some PGR treatments increased the number of new nodes on bearing shoots on ‘ON” trees to values equal to those of nonbearing shoots of ‘OFF’ crop control trees (Table 1, asterisk). Identify the better treatments. On average two additional nodes of growth were added to shoots in all treatments from February through April. Thus, in April shoots treated with some PGRS (Table 1, shaded) remained longer than bearing or nonbearing shoots on ‘ON’ crop control trees and equal to nonbearing shoots on ‘OFF’ crop control trees. This result suggests that with regard to increasing vegetative shoot growth there was no advantage derived from supplementing the Summer PGR treatment with the second Spring PGR treatment. However, the effect of the Spring PGR treatments on floral bud break and return bloom and fruit set remains to be determined.

Table 1. The effect of scaffold branch injected plant growth regulator treatments on vegetative shoot growth, as number of new nodes produced.
		New Nodes
Treatment	Branch Status	July-February	July-April
ON Control	Fruit	0.8 l	3.3 jkl
TIBA+6BA SUMMER	Fruit	2.3 hijk*	4.6 cdefghij
TIBA+PCK SUMMER	Fruit	2.5 ghij*	4.9 bcdefghij
NATI+6BA SUMMER	Fruit	2.7 fghij*	4.2 fghijkl
NATI+PCK SUMMER	Fruit	2.2 hijk*	3.9 hijkl
TIBA SUMMER	Fruit	2.4 hij*	4.9 bcdefghij
NATI SUMMER	Fruit	2.5 fghij*	4.3 efghijkl
6BA SUMMER	Fruit	2.2 ijkl	4.2 fghijkl
PCK SUMMER	Fruit	2.6 fghij*	4.7 cdefghij
TIBA+6BA SUMMER+SPRING	Fruit	2.4 hij*	4.5 defghijk
TIBA+PCK SUMMER+SPRING	Fruit	3.0 efghi*	4.5 defghij
NATI+6BA SUMMER+SPRING	Fruit	2.6 fghij*	5.0 abcdefghij
NATI+PCK SUMMER+SPRING	Fruit	2.2 ijk*	3.7 ijkl
TIBA SUMMER+SPRING	Fruit	2.0 ijkl	4.1 ghijkl
NATI SUMMER+SPRING	Fruit	3.1 defghi*	5.5 abcdefghi
6BA SUMMER+SPRING	Fruit	2.7 fghi*	4.9 bcdefghij
PCK SUMMER+SPRING	Fruit	1.3 jkl	2.5 l
OFF Control	No Fruit	3.6 abcdefgh	5.0 bcdefghij
ON Control	No Fruit	1.0 kl	2.7 kl
TIBA+6BA SUMMER	No Fruit	3.8 abcdefg	4.7 cdefghij
TIBA+PCK SUMMER	No Fruit	4.7 ab	5.9 abcdefg
NATI+6BA SUMMER	No Fruit	4.8 a	6.3 abcd
NATI+PCK SUMMER	No Fruit	4.5 abc	6.0 abcde
TIBA SUMMER	No Fruit	4.4 abcd	6.0 abcdef
NATI SUMMER	No Fruit	4.2 abcde	4.9 bcdefghij
6BA SUMMER	No Fruit	3.4 bcdefghi	4.0 hijkl
PCK SUMMER	No Fruit	4.3 abcde	5.5 abcdefghi
TIBA+6BA SUMMER+SPRING	No Fruit	4.2 abcde	5.2 abcdefghi
TIBA+PCK SUMMER+SPRING	No Fruit	4.8 a	5.7 abcdefgh
NATI+6BA SUMMER+SPRING	No Fruit	3.9 abcdef	5.1 abcdefghi
NATI+PCK SUMMER+SPRING	No Fruit	3.2 cdefghi	4.2 efghijkl
TIBA SUMMER+SPRING	No Fruit	4.8 a	6.5 ab
NATI SUMMER+SPRING	No Fruit	4.5 abc	6.8 a*
6BA SUMMER+SPRING	No Fruit	4.8 a	6.4 abc
PCK SUMMER+SPRING	No Fruit	3.6 abcdefgh	4.7 cdefghij
P-value		<0.0001	<0.0003
Note: shading denotes treatments significantly different than ON Control + Fruit treatment. Asterisk denotes treatments significantly different than OFF Control (- Fruit).

 

Summary

These preliminary data demonstrate that PGRs increase shoot growth, which might result in more nodes with the potential to produce inflorescences the following spring. Future studies are anticipated to address the use of promising treatments in foliar applications. Naturally-occurring compounds, such as PCK and NATI, may be easier and less costly to register than PGRs, which are classified as pesticides. Therefore, significant growth response to the natural compounds tested may have commercial benefit even if proven less efficacious than the synthetic PGRs.

Acknowledgements: The financial support of the California Olive Committee and the technical support of the Lindcove Research and Extension Center were integral to the success of this project.

 

 

 

 

 

 

 

olive tree

Alternate Bearing in Mandarin – The basics

Alternate bearing is typically initiated by adverse climate. Once initiated, in the absence of additional environmental constraints affecting crop load, the bearing status of an orchard alternates between ON and OFF years, with ON years exhibiting less vegetative growth than OFF years.  This biennial cycle, however, can be reset by adverse environmental conditions affecting bloom and fruit set.  Adverse conditions 8-10 weeks prior to bloom may cause abortion of female flower parts, resulting in a high proportion of staminate (male) flowers that do not give rise to fruit.  Additionally, adverse weather conditions at bloom may impact pollination and subsequent fruit set.  Any conditions resulting in loss of crop during an anticipated ON year may render the season an OFF year. 

For a fuller discussion of this topic, see the full article by Carol Lovatt at:

http://ceventura.ucanr.edu/newsletters/Topics_in_Subtropics45348.pdf

The Topics in Subtropics Newsletter

 

mandrain

Research Advances on Mitigation of Alternate Bearing in Olive

Alternate or biennial bearing is a phenomenon where fruit production alternates between large crops consisting of smaller, lower value fruit during an "ON" year and smaller crops consisting of larger, higher value fruit during an "OFF" year.  Alternate bearing is not unique to olive, but also affects other perennial California crops including (but not limited to) pecan, pistachio, apple, avocado and citrus, especially mandarins.  The large swings in biennial fruit production impact the overall industry, from growers to harvesters, to processors.  The 2009-2011 seasons exemplify the magnitude of the affect of alternate bearing on olive production and crop value in Tulare County (Table 1). 

 

Table 1. Tulare County Olive Production

	Yield (Tons/Acre)	Value (Dollars)
2009 OFF	0.40	5,750,000
2010 ON	7.23	74,128,000
2011 OFF	1.82	23,278,000

 

Causes of alternate bearing in olive

In olive, the current year's fruit is borne on the prior year's vegetative growth.  The current year's fruit, and specifically the pit, inhibits the vegetative growth that supports flower buds for the following year (Sibbett 2000).  Consequently, during an ON year, fruit production directly inhibits vegetative growth.  A recent Israeli study (Dag et al 2010) demonstrates the inhibitory effect of fruit on vegetative shoot growth and return bloom in the oil cultivar 'Coratina'. Similarly, in 2011 and 2012 we investigated the relationship between fruit load and vegetative growth on 'Manzanillo' olives in Tulare County.  In our study, we assessed the influence of fruit on vegetative growth on ON trees in comparison to OFF trees.  Additionally, within ON trees, we assessed vegetative growth on branches bearing fruit and branches not bearing fruit. Our study demonstrated the inhibitory effect of fruit number (crop load) on vegetative growth (Table 2).  Vegetative shoot growth was lower for shoots that did not set fruit (-fruit) on ON trees than shoots –fruit on OFF trees indicating a whole-tree effect of crop load in alternate bearing.  Additionally, our data demonstrate that fruit-bearing branches exhibit even less vegetative growth than non-fruit-bearing branches on ON trees, providing evidence of a strong localized effect of fruit on shoot growth (Table 2). 

 

Our studies also demonstrated that the bearing status of a shoot influences the following year’s percent bud break of floral buds.  For example, shoots bearing fruit in 2011 exhibited over 90% fewer inflorescences than did shoots without fruit, regardless of whether non-bearing shoots were on an ON-or OFF- tree. 

 

Table 2. Effect of ON- and OFF-crop tree status and the presence (+fruit) or absence (-fruit) of fruit set on a shoot on shoot extension growth. (Orchard 2, Exeter, CA, 2011).

       ^z Values in a vertical column followed by different letters are significantly different at 

         specified P levels by Fisher’s LSD Test.

 

Alternate bearing is typically initiated by adverse climate. Once initiated, in the absence of additional environmental constraints affecting crop load, the bearing status of an orchard alternates between ON and OFF years, with ON years exhibiting less vegetative growth than OFF years.  This biennial cycle, however, can be reset by adverse environmental conditions affecting bloom and fruit set.  Adverse conditions 8-10 weeks prior to bloom may cause abortion of female flower parts, resulting in a high proportion of staminate (male) flowers that do not give rise to fruit.  Additionally, adverse weather conditions at bloom may impact pollination and subsequent fruit set.  Any conditions resulting in loss of crop during an anticipated ON year may render the season an OFF year. 

 

Mitigation of Alternate Bearing

Reduction of fruit load prior to the major period of vegetative shoot growth during an ON year may mitigate alternate bearing.  Chemical thinning with NAA at bloom may result in a smaller crop with larger sized fruit during an ON year, and allow for more vegetative growth to support the following year's crop. 

 

Current Research on Mitigation of Alternate Bearing using Plant Growth Regulators (PGRs)

During the 2012 growing season, we investigated the potential for applications of PGR treatments to mitigate alternate bearing in olive.  The specific goal of PGR treatments was to enhance spring bud break, summer vegetative shoot growth, and return bloom.  In the first phase of this project, individual scaffolds of mature ‘Manzanillo’ olives were injected with a suite of PGR treatments. PGR treatments were injected at two points during the growing season, with winter/spring (pre-bloom) treatments targeting floral bud break, and summer treatments targeting vegetative shoot growth.  Additionally, the winter/spring injections were introduced over a four month timeframe (January-April) to assess the optimal timing of injections for enhanced floral bud break. Scaffold injection treatments resulting in desired growth responses will be carried forward in future studies focused on determining compound efficacy in foliar applications.  Treatments included either of two auxin transport inhibitors (tri-iodobenzoic acid and naringenin) injected alone, or in combination with two cytokinins (6-benzyladenine, and a proprietary cytokinin).

 

In the 2012 growing season, PGR treatments had encouraging results.  Cytokinin treatments injected in February resulted in over 60% more floral bud break on non-bearing shoots of ON- trees, as compared to the untreated control.  Similar treatments also increased floral bud break over 6 fold on bearing shoots on ON-trees; however, due to the variability in floral bud break, there was no significant difference between treated trees and controls on bearing shoots on ON-trees.    All summer PGR treatments (either auxin transport inhibitors or cytokinins, alone or in combination)  increased vegetative shoot growth on both bearing and non-bearing branches  by over four fold; however, the influence of PGR-induced enhancement of summer vegetative growth on return bloom is not yet known.  Return bloom and fruit set will be quantified during the 2013 season to determine the efficacy of PGR treatments on mitigation of alternate bearing on olive.   

 

Selected Literature

Dag, A., Bustan, A., Avni, A., Tzipori, I, Lavee, S., Riov, J. 2010. Timing of fruit removal affects concurrent vegetative growth and subsequent return bloom and yield in olive (Olea europaea L.). Scientia Horticulturae 123:469-472.

 

Sibbett, S. 2000. Alternate bearing in olive trees. California Olive Oil News. Vol. 3, Issue 12.

olives

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