Flower anatomy and pollination in tree crops
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2/23/2014 Flower anatomy and pollination in tree crops Lecture outline 1. Flower anatomy – – Structures within a flower Perfect flowers, imperfect flowers, monoecy, and dioecy 2. Flower and fruit development – – Vegetative and floral tissue Floral bud development and fruit quality problems 3. Pollination – – – – – Brooke Jacobs Associate Specialist Department of Plant Sciences, UC Davis Flower anatomy Pollination and common modes of pollen transport What happens after pollination? Effective Pollination Period (EPP) Fruit and nut quality issues related to pollination Mechanisms that limit self‐pollination 4. Link between flower and fruit anatomy – – Three primary flower “types” Fruit anatomy Flower anatomy 1 2/23/2014 Flower anatomy Perfect and imperfect flowers stamen (anther and filament) Male flower Pistil (style, stigma and ovary) “Perfect” flower receptacle Female flower Examples of imperfect flowers in tree crops Monoecious vs. dioecious species OR Walnut Pistachio Kiwifruit Monoecious species ‐ individuals are all hermaphrodites ‐ can have perfect or imperfect flowers 2 2/23/2014 Monoecious vs. dioecious species Pollen transfer in monoceious species AND Dioecious species ‐ individuals are either male or female Pollen transfer in monoceious and dioecious species Pollen only has to travel short distances in monoecious species to fertilize an ovule. Lecture outline 1. Flower anatomy – – Structures within a flower Perfect flowers, imperfect flowers, monoecy, and dioecy 2. Flower and fruit development – – Vegetative and floral tissue Floral bud development and fruit quality problems 3. Pollination – – – – – Pollination and common modes of pollen transport What happens after pollination? Effective Pollination Period (EPP) Fruit and nut quality issues related to pollination Mechanisms that limit self‐pollination 4. Link between flower and fruit anatomy Pollen travels longer distances in dioecious species to fertilize an ovule. – – Three primary flower “types” Fruit anatomy 3 2/23/2014 Two primary tissue types Two primary bud types vegetative Peach vegetative Peach floral vegetative floral Cherry Pistachio floral Almond Lateral bearing on shoots and spurs Peach: lateral bearing on one year old shoots Pome fruits: mixed buds with leaves and several flowers borne on the terminal tips of shoots Stone fruits: simple buds are borne laterally with single (peach) or multiple (plum, cherry) flowers Spurs are like miniature branches Almond and cherry: lateral bearing on spurs 4 2/23/2014 Meristem produces vegetative and floral buds Floral buds derive from vegetative meristem Inside developing buds all growth comes from a terminal cluster of cells called apical meristem Vegetative apical meristem form bud scales and leaves A case study: Sweet cherry flower bud differentiation Vegetative meristem also develops into floral buds A case study: Sweet cherry flower bud differentiation Prof. Polito Scanning electron microscope view of apical meristem in sweet cherry In mid‐summer the shoot apex of a flower bud begins to produce primordial flowers 5 2/23/2014 A case study: Sweet cherry flower bud differentiation As the flowers develop, sepal primordia initiate at the flanks of the floral meristem A case study: Sweet cherry flower bud differentiation A case study: Sweet cherry flower bud differentiation About one week after sepals are initiated, petal primordia form inside the sepals A case study: Sweet cherry flower bud differentiation Stamens are initiated next, leaving a broad base of undifferentiated meristem where the pistil forms 6 2/23/2014 A case study: Sweet cherry flower bud differentiation A case study: Sweet cherry flower bud differentiation ‐ Pistil begins as an open structure that grows at the margins ‐ Forms from the base of undifferentiated cells usually consuming all of the meristem. A case study: Sweet cherry flower bud differentiation Eventually the margins grow together to form a closed locule that defines the ovary. Timing of floral bud development Summer • When the margins come into contact they fuse, forming a suture. • Developmental failures lead to aberrant fruits. • Abnormal development typically occurs when trees are stressed during these stages of flower development. Fall Winter Spring 7 2/23/2014 Flower bud development and fruit quality Spurred and double fruits occur when multiple pistils develop within a bud. Flower developmental stage Fruit developmental abnormality Lecture outline 1. Flower anatomy – – Structures within a flower Perfect flowers, imperfect flowers, monoecy, and dioecy Flower bud development and fruit quality “Zippering” and “incomplete sutures” occur when two sides of the carpel do not fuse properly. Flower developmental stage Fruit developmental abnormality Pollination and pollen transfer Pollination: transfer of pollen from anther to a stigma 2. Flower and fruit development – – Vegetative and floral tissue Floral bud development and fruit quality problems 3. Pollination – – – – – Pollination and common modes of pollen transport What happens after pollination? Effective Pollination Period (EPP) Fruit and nut quality issues related to pollination Mechanisms that limit self‐pollination 4. Link between flower and fruit anatomy – – Three primary flower “types” Fruit anatomy Insects and wind are the two primary modes of pollen transport in fruit and nut tree crop species grown in California. 8 2/23/2014 Insect pollinated flowers Almond Wind pollinated flowers Pomegranate Olive Plum Kiwifruit Insect pollinated flowers typically have showy petals, nectar and scent Pollen capture in wind pollinated flowers Walnut Wind pollinated flowers typically: ‐ Lack petals, nectar and scent ‐ Large feathery stigmas to catch pollen from air flow ‐ Large exerted anthers Similarities between walnut and peach flowers Microscale wind tunnel experiments ‐ pollen is not captured at random ‐ shape and form of the flower structures create air flow patterns that direct the pollen to the stigma surfaces Walnut (wind pollinated) Prunus (insect pollinated) 9 2/23/2014 Crop Flower type Dioecious or monoecious? Pollen transport Almond Perfect monoecious Apple perfect monoecious insect (supplemental pollinator required) Apricot perfect monoecious insect Cherry Fig Kiwifruit Olive Peach & Nectarine insect (supplemental pollinator required) perfect monoecious insect (supplemental pollinator required) imperfect dioecious wasp (supplemental pollinator required) imperfect* dioecious* insect (supplemental pollinator required) both perfect & imperfect** monoecious wind perfect monoecious insect Pear perfect monoecious insect (supplemental pollinator required) Pecan imperfect monoecious wind both perfect & imperfect monoecious & dioecious*** insect Plum perfect monoecious insect (supplemental pollinator required) Prune perfect monoecious insect (supplemental pollinator required) imperfect dioecious wind Pomegranate perfect monoecious insect (supplemental pollinator required) Quince perfect monoecious insect Walnut imperfect monoecious wind Persimmon Pistachio Pollen and pollination What happens after pollination? Pollen is released from the anther as a dehydrated cell. When pollen lands on a stigma it rapidly hydrates in the fluid present on the stigma surface. Effective Pollination Period (EPP) Effective Pollination Period: Term used to describe the timing of three separate conditions required for the successful fertilization of an ovule. Pollination: pollen lands on stigma 2. Pollen tube grows down style 1. Pollen tube germinates 3. Pollen fertilizes an ovule 10 2/23/2014 Effective Pollination Period (EPP) Effective Pollination Period (EPP) 1. Stigma receptivity: ability of the stigma to support pollen germination 3. Ovule viability: time period when the ovule is capable of being fertilized 2. Pollen tube growth rate: time required for pollen tubes to grow through the style stigma style Effective Pollination Period (EPP) Stone fruit 2 ovules Pome fruit 10 ovules in 5 ovaries Effective Pollination Period (EPP) Temperature effects on stigma receptivity and pollen tube length in almond and peach EPP 55 68 55 68 80 F 80 F Pollen dispersal Stigma receptivity Ovule receptivity March 1st March 5th March 10th X March 15th March 20th Pollen tube growth from stigma to ovule = 5 days 11 2/23/2014 Effective Pollination Period (EPP) Effective Pollination Period (EPP) Temperature effects on stigma receptivity and pollen tube growth rates in two varieties of prune EPP Pollen dispersal Stigma receptivity X Ovule receptivity Pollen germination: 50 – 90oF Optimum temperature: 72o F Pollen tube growth: 55 – 95oF Optimum temperature:75o F Effective Pollination Period (EPP) March 1st Effective Pollination Period (EPP) This can dramatically reduce the EPP in a given year EPP Pollen dispersal Pollen dispersal Stigma receptivity Stigma receptivity X X Ovule receptivity March 5th March 15th March 20th March 10th Pollen tube growth from stigma to ovule = 5 days High temperatures can reduce stigma and ovule receptivity March 1st March 5th March 10th March 15th March 20th Pollen tube growth from stigma to ovule = 5 days March 1st March 5th X Ovule receptivity March 10th March 15th March 20th Pollen tube growth from stigma to ovule = 5 days 12 2/23/2014 Effective Pollination Period (EPP) Effective Pollination Period (EPP) EPP EPP High heat during bloom is associated with poor fruit set in prune Pollen dispersal Pollen dispersal Stigma receptivity X X March 1st March 5th Temperature can also affect pollen dispersal timing and pollen tube growth rate. Stigma receptivity X X X Ovule receptivity March 10th March 15th March 20th March 1st Pollen tube growth from stigma to ovule = 5 days ‐ Developing seeds provide signals to accessory tissue to develop ‐ Insufficient pollination results in small and/or asymmetrical fruit Ovule receptivity March 10th March 15th March 20th Pollen tube growth from stigma to ovule = 5 days Relationship between pollination and quality Insufficient pollination: March 5th X Parthenocarpy Parthenocarpy: Production of fruit without fertilization of ovules (seedless fruit) ‐ Persimmon is commonly planted in solid blocks far away from other trees to encourage parthenocarpy 13 2/23/2014 Parthenocarpy Effect of excessive pollination on fruit set California Pistillate Flower Abortion (PFA) in walnut Oregon PFA results in a loss of fruitlets early in the season (2‐3 weeks after bloom) ‐ ‐ ‐ Bartlett pears in Sacramento Delta and Clearlake , CA and produce parthenocarpic fruit In other growing regions, including Oregon, Bartlett requires cross pollination and fertilization to produce fruit Consistent differences in fruit shape between California and Oregon Bartlett pears Effect of excessive pollination on fruit set Prof. Polito Effect of excessive pollination on fruit set Pistillate Flower Abortion (PFA) in Serr walnut Pistillate Flower Abortion (PFA) in Serr walnut 5 days after bloom 12 days after bloom 14 2/23/2014 Effect of excessive pollination on fruit set % PFA Pistillate Flower Abortion (PFA) in walnut PFA decreases with distance from pollen source PFA positively correlated with pollen load PFA greatest in Serr, but also occurs in Chandler and Vina varieties Mechanisms that limit self pollination in plants Mechanism to limit self‐pollination: Flower anatomy Self pollination: pollen is transferred from the anther to a stigma within the same individual 1. Flower anatomy 2. Spatial separation of imperfect flowers 3. Temporal separation 4. Self incompatibility Why might it be advantageous for plants to have mechanisms which prevent pollination/fertilization? Example: “heterostyly” Example: prune Chasmogamous flowers: anatomy that limits self‐pollination 15 2/23/2014 Mechanism to limit self‐pollination: Flower anatomy Mechanism to limit self‐pollination: Dioecy Cleistogamous flowers: anatomy that facilitates self‐ pollination Spatial separation: separate male and female individuals (technical term: dioecy) ex. pistachio, kiwifruit, and some persimmon Mechanism to limit self‐pollination: Dichogamy Mechanism to limit self‐pollination: Self incompatibility Does all pollen transferred to a stigma result in fertilization and fruit development? Temporal separation: male and female organs mature at different times (technical term: dichogamy) example: walnuts Chart from www.BurchellNursery.com 16 2/23/2014 Mechanism to limit self‐pollination: Self incompatibility Mechanism to limit self‐pollination: Self incompatibility Does all pollen transferred to a stigma result in fertilization and fruit development? Not necessarily Self incompatibility: the inability of a flower to support growth of pollen from the same tree or cultivar ‐ Gametophytic self incompatibility determined by the “S” locus ‐ Pollination occurs when the allele carried by a pollen grain is different from either of the alleles in the stigma ‐ Pollen with the same allele as those in the stigma is rejected Possible Progeny: None S1S3, S2S3 S1S3, S1S4, S2S3, S2S4 Example of gametophytic self incompatibility Self incompatibility in fruit and nut tree crops Stone fruit ‐ Peach, nectarine and apricot are self compatible Managing self incompatibility 1. Plant compatible pollinizer cultivars along with the primary fruit bearing cultivar ‐ Sweet cherry, almond and plum are self‐incompatible Pome fruit ‐ Apples are partially self incompatible and require pollinizers for optimum fruit size and quality. ‐ Some apple cultivars accept self pollen at the end of bloom. ‐ Pears are self‐incompatible (but in some areas most fruit produced is parthenocarpic) Other ‐ Olives are self compatible at low temperatures but reject self‐pollen at high temperatures Pollinizer row trained to a single upright trunk Pollinizer cultivar grafted onto center of fruiting cultivar 17 2/23/2014 Managing self incompatibility 2. Select compatible cultivars with sufficient overlap in bloom time. Managing self incompatibility 3. Orchard layout must facilitate pollen flow. Honeybees tend to fly up and down rows, not across. Main Variety Compatible Variety 1 Compatible Variety 2 Example almond orchard layout Managing self incompatibility Managing self incompatibility 4. Supplemental honey bees to ensure effective movement of pollen among compatible cultivars. Main Variety Compatible Variety 1 Compatible Variety 2 New release, success to be determined. 18 2/23/2014 Managing self incompatibility Lecture outline 1. Flower anatomy Pollen for sale! – – Structures within a flower Perfect flowers, imperfect flowers, monoecy, and dioecy 2. Flower and fruit development – – Vegetative and floral tissue Floral bud development and fruit quality problems 3. Pollination – – – – – Pollination and common modes of pollen transport What happens after pollination? Effective Pollination Period (EPP) Fruit and nut quality issues related to pollination Mechanisms that limit self‐pollination 4. Link between flower and fruit anatomy – – Link between flower and fruit anatomy Three primary flower “types” Fruit anatomy Three primary flower types Three primary flower types in California tree crops: 1.Perigynous 2.Epigynous 3.Hypogynous Hypanthium: tissue composed of fused petals, sepals, and stamen 19 2/23/2014 1. Perigynous flowers 1. Perigynous flowers Hypanthium forms a cup‐like structure surrounding, but not attached to, the ovary After fertilization the hypanthium is shed when the ovary develops into fruit tissue. As a result, petals and stamen do not remain attached to the fruit. 1. Perigynous flowers Fruit associated with perigynous flowers Perigynous fruit develop from a single carpel and contain one or two seeds. Examples: peach, olive, cherry, plum, apricot and almond 20 2/23/2014 2. Epigynous flowers 2. Epigynous flowers After fertilization the hypanthium develops into fruit tissue. The ovary is inferior and fused to the hypanthium tissue. 2. Epigynous flowers Remnants of the sepals, stamen and style remain attached to the fruit. 2. Epigynous flowers Epigynous fruit develop from multiple fused carpels and contain more than two seeds and accessory tissue. Examples: apple, pear and quince 21 2/23/2014 3. Hypogynous flowers 3. Hypogynous flowers Hypogynous flowers lack a hypanthium. After fertilization the ovary develops into fruit tissue. Instead, the petals, stamen and sepals arise from the receptacle below the ovary. The sepals remain attached to the base of the fruit and receptacle. 3. Hypogynous flowers 3. Hypogynous flowers Hypogynous fruit develop from multiple fused carpels and contain more than two seeds. Examples: persimmon and kiwifruit 22
