Title. Integrating Fasciculate and Fruit Abscission into Jalapeņos
PD: Allen Van Deynze, Research Director, Seed Biotechnology Center, University of California, Davis, Email: avandeynze@ucdavis.edu
co-PDs:
Theresa Hill (Specialist) Seed Biotechnology Center, University of California, Davis
Overall hypothesis and goal: We have screened a set of wild and semi-domesticate accessions recently collected in regions of Mexico for disease resistance and horticultural traits. Among these is a semi-domesticated C. annuum accession, UCD-14 with oblong fruit with firm texture that easily abscises when picked leaving the pedicel behind. We also have lines carrying the fasciculate mutation conferring determinant flowering in pepper. Our goal is to integrate fruit abscission into an advanced jalapeno breeding line alone and in combination with fasciculate mutation in pepper to investigate their potential for mechanical harvesting.
- Significance to US Agriculture
- Research
- Determine the inheritance of abscission of fruit in UCD-14 populations
- Introgress abscission in advanced jalapeno lines.
- Study the effect of abscission trait on fruit quality alone and in conjunction with the fasciculate (fa) mutation.
- The effect of the UCD-14 abscission trait on fruit quality will be evaluated in 3 pepper backgrounds, jalapeno, anaheim, and blocky.
- Populations will be developed to study this trait in conjunction with the determinate growth habit fa single gene in F2s. In 2015, F2 seed will be generated as well as BC1 seed with fa and advanced jalapeno breeding line.
The US Pepper industry was valued at $810 M grown on 71,200 acres in 2013 [61] of which bell peppers represent 72% of the value. California grows 47% of peppers in the US. The majority of varieties are hybrids developed by private industry with open-pollinated varieties released from public sources also used in organic production. Public breeding programs are essential to focus on introducing and characterizing germplasm with novel and difficult to measure traits as well as training students for the industry.
Mechanical harvesting has been identified as a goal for the pepper industry by the California Pepper Commission. Mechanical harvesting requires a combination of harvesters and varieties that are amenable and can tolerate the process and maintain yield and quality. Several traits are essential including uniform ripening and thick pericarp, tolerant of bruising and breakage. Although, some blocky types are currently harvested mechanically with significant labor required for sorting, these go into the low value processing markets. The tomato industry was revolutionized by the combination of the self-pruning, determinate trait and the Jointless gene conferring abscission of the pedicel in the tomato. The processing tomato industry in California commands >95% of the US market valued at $800 M annually. With increasing cost and decreasing availability of labor needed to pick peppers, a similar innovation could give California and US farmers significant returns and potential increase in pepper industry in California, the ultimate goal is to have fresh market quality and mechanical harvesting in both blocky and hot types.
While a mutation in fasciculate (fa), the ortholog to the tomato self-pruning gene, gives a similar determinate phenotype in pepper, the jointless gene does not result in abscission of fruit in pepper. The fa mutation, commonly found in ornamental peppers, confers significantly reduced secondary internode length and vestigial leaves resulting in a phenotype with multiple fruit clustered and determination of flowering branches, i.e. a uniform ripening determinate phenotype that is early maturing (Elitzur et al 2009). Unlike tomato, the jointless mutation in pepper is antagonistic to FA resulting in late flowering and addition of a leaf in the sympodial unit and no floral clusters (Cohen et al. 2012). The same phenotype is observed in the jointless/fa double mutant. The proposed S locus in pepper confers a pleiotropic effect of undesirable softening of pericarp at maturity along with a reduced abscission layer, thus easy removal of the pedicel during picking. The proposed enzyme responsible is polygalacturonase (Rao and Paran 2003). Wild peppers often have the S locus traits. Unlike the S locus, we have identified a semi- domesticated pepper accession, UCD-14, having fruit that is easily removed from the pedicel while retaining firmness (Fig. 1). We predict that combining this trait with the fa mutation (Fig 2) will improve mechanical harvesting of pepper.
Figure 1. Longitudinal and cross section of UCD-15 showing pericarp thickness. Note clean abscission break at calyx end.
Figure 2. Fasciculate (fa) mutation in pepper showing reduced internode length and and cluster of fruit grown at UCD.
Timeline: May 1, 2014-April 30, 2015
Specific objectives:
Approach
UCD-14 seems to separate the softening and abscission trait associated with the proposed polygalacturonase gene at the S locus (Fig 1). The phenotype of the UCD-14 semi-domesticated line provides a unique opportunity to introduce easily abscising fruit trait with determinate habit, both desirable traits for mechanical harvesting.
Objective 1. To study the inheritance of fruit abscission and develop closely linked DNA markers to further select the trait we have created a single F2 population of greater than 150 plants from UCD-14 x Early Jalapeno. This population will be grown in the field in summer 2015 at UC Davis and evaluated for plant architecture, ease of fruit abscission for 5 green and 5 ripe fruit per plant, fruit size (length, width and weight), fruit softness and pericarp thickness at maturity. Segregation of the trait will be tested using X2 goodness fit of test for one and two gene models. Frequency of this trait in populations suggests a simple inheritance. Furthermore, as part of a supporting project on two populations with 100-150 F3 families each, UCD-14 x NuMex Garnet (anaheim type) and UCD-14 x Maor (blocky type), we will measure the same traits in 8 plants/family in the field at UC Davis. These lines are being genotyped using genotype-by- sequencing. As a result, tightly linked markers and supporting measures of heritability will be achieved.
Objective 2. To introgress the abscission trait into an advanced jalapeno breeding line (selection from the UC Davis breeding program) the F1 of UCD-14 x Early Jalapeno will be crossed and backcrossed to BC2 and selfed. Furthermore the F1 will be crossed to a line with the fa mutation and selfed. As a backup, the fa mutation will be crossed and backcrossed into the advanced jalapeno line.
Objective 3. Future Research.
Deliverables and expected Outcomes.
We expect to gain understanding of the inheritance and expression of the abscission trait introgressed from UCD-14 into jalapeno. We will also evaluate its effect on fruit quality, maturity and plant architecture in multiple pepper genetic backgrounds establishing the value of the trait in the pepper industry. We will create populations to study the combination of abscission and the fasciculate mutation for determinacy in pepper. Both traits have potential to create pepper lines amenable to mechanical harvesting.
|
Budget |
Total ($) |
|
Personnel |
12,000 |
|
Equipment |
0 |
|
Supplies |
3,000 |
|
Travel |
0 |
|
Indirect |
0 |
|
Total |
15,000 |
Budget justification: We are requesting $12,000 for a part-time (15%) research associate to aid in crosses and plant maintenance. We are requesting $3000 supplies and fees for greenhouse, soil, and field costs for carrying out trials and advancing populations. Genotyping costs are being covered by alternate funds. Funds for main personnel-supervising technician are from other sources. No funds are required for salaries for PIs who will manage the project.
References
Cohen O., Borovsky Y., David-Schwartz R., Paran I. (2012) CaJOINTLESS is a MADS-box gene involved in suppression of vegetative growth in all shoot meristems in pepper. J Exp Bot. DOI: 10.1093/jxb/ers172.
Elitzur T, Nahum H, Borovsky Y, Pekker I, Eshed Y, Paran I. Co-ordinated regulation of flowering time, plant architecture and growth by FASCICULATE: the pepper orthologue of SELF PRUNING. Journal of Experimental Botany 2009;60(3):869-880.
Rao G.U., Paran I. (2003) Polygalacturonase: a candidate gene for the soft flesh and deciduous fruit mutation in Capsicum. Plant Molecular Biology 51:135-141. DOI: 10.1023/a:1020771906524.
USDA. 2011. National Agricultural Statistics Service.