Pummelo (Citrus grandis) production in south Florida

Jonathan H. Crane, Tropical Fruit Crop Specialist

University of Florida, IFAS

Tropical Research and Education Center, Homestead

Botany of pummelo

• Rutaceae

• Numerous important fruit crops within the Rutaceae including orange, grapefruit, lime, tangerine, tangerine hybrids, Key lime, and kumquat

• Origin –Southeast Asia (Malay Archipelago)

• Thrives in warm to hot climates

• Distribution – throughout the tropical and subtropical world

• Commercial production in Thailand, the Philippines, and others

Botany

• Medium to large trees to 16-50 ft (5-15 m) tall• Grafted trees have one or more major deep roots

(rootstock dependent). However, >90% of the fibrous root system is probably within 12-18 inches (30-45 cm) soil surface.

• Evergreen – flushing rate and frequency is influenced by temperature and available soil moisture; 10 or more flushes per year; leaf abscission rate is influenced by climate and disease and insect pressure

• Leaves are characterized by a pronounced wing• Inflorescence axillary, with a cluster of a few flowers or

a single flower; large flowers• Fruit matures 7-12 months after flowering

•Pummelo fruit is a hesperidium berry with a thick, leathery exocarp (albedo:peel) surrounding the flavedo which possesses 12-18 segments with juice vesicles. Fruit 4-12 inches (10-30 cm) in dia.; shape may be pyriform or globose; the peel is green to yellow.

Botany

Climatic adaptations – estimated optimum

• Shoot growth, 59-97oF (15-36oC)

• Root growth, 59-86oF (15-30oC)

• Floral induction occurs after a quiescent period due to cool temperatures (<55oF;<13oC) and/or drought (>3 weeks) any time of the year. Major flowering is during spring/summer. Major harvest fall/winter.

• Optimum temperatures during flowering, 70-95oF (21-35oC)

• Optimum temperature range for fruit growth, 75-95oF (24-35oC)

Optimum climatic scenario

• Optimum flowering and fruiting occurs in tropical and warm subtropical climates where vegetative growth ceases due to cool temperatures (dry conditions are beneficial), followed by moderately warm temperatures in spring during the flowering period, followed by moderately high temperatures during fruit development

• The major harvest season is fall/winter although there may be a small crop during spring

• Whether off season flowering may be induced in Florida by exposure to drought followed by high soil moisture is not known

Site selection and soils

• Mediterranean, semi-arid, winter rainfall pattern areas (California, Israel)

• Humid subtropical areas with summer rainfall pattern (Mexico)

• Semitropical/warm subtropical areas with summer rainfall pattern (Florida)

• Tropical lowland areas (Mexico, Puerto Rico, Southeast Asia)

• Exposure to cool/cold non-freezing temperatures or drought during fall/winter

• Many well drained soil types, ideal pH 5.5-7.0, with moderate fertility

• Low freeze tolerance. Less cold hardy than ‘Tahiti’ lime

Orchard/grove infrastructure

• Land preparation – clearing, leveling or sloping and/or bedding, ditches/ canals

• Grove layout – NS is preferred for optimum duration of light exposure; for some land parcels it is more efficient for equipment and movement for rows to be oriented in EW direction

• Irrigation system(s) installation – for watering and possibly fertilizing; microsprinkler or drip; for cold protection use high volume

• Wind machines for cold protection in areas with predominantly radiation type freezing events

Pummelo cultivars

• Numerous cultivars exist, most in Thailand

• ‘Hirado Buntan’ is the major Florida cultivar

• ‘Chandler’ – pink flesh

• ‘Kao Panne’ – white-fleshed

• ‘Oroblonco’ (http://www.ccpp.ucr.edu/variety/309.html)

• ‘Goaliath’ – white-fleshed

• ‘Mato’ – white-fleshed

• ‘Shatinyu’ – white-fleshed

• ‘’Kao Teang Kwaa’

• ‘Som Tha Khoi’

• ‘Som Thubthim’

• ‘Melogold’ (http://www.ccpp.ucr.edu/variety/323.html)

Information sources

• Verheij, E.W.M. and R.E. Coronel (editors). 1992. Plant Resources of South-East Asia. PROSEA, Bogor, Indonesia.

• Morton, J.F. 1987. Fruits of warm climates. Creative Resource Systems, Inc., Winterville, NC.

• Davies, F.S. and L.G. Albrigo. 1994. Citrus. CAB International, United Kingdom

• Germplasm catalogue of germplasm in Nepal (http://www.soton.ac.uk/~icuc/pumgerm/pum-top.htm)

• Univ. of Calif., Citrus Clonal Protection Program (http://www.ccpp.ucr.edu/variety/grapefruits.html)

• USDA-GRIN database (USDA-GRIN database (http://www.ars-grin.gov/npgs/tax/index.html)

Pummelo propagation and rootstocks

• Marcottage (airlayering)

• Grafted to rootstocks by

– T-bud budded

– Veneer and cleft grafted

• Rootstock choice depends upon– Soil factors– Disease factors– Effect on fruit

production, tree vigor, and longevity

• Rootstocks – pummelo seedlings; needs testing

Plant spacing in Florida

• Factors

– Life expectancy of the grove

– Climate

– Tree vigor

– Ultimate tree size desired

– Presence of irrigation system

• Range 10-20 ft (3.1 m-6.1 m in-row; 15-25 ft (4.6 m-7.6 m) between-row

• Recommended: 15 ft (4.6 m) in-row and at least 20 ft (6.1 m) between rows

Estimated requirements for optimum flowering and fruiting

• Exposure to cool non-freezing temperatures (<55oF;<13oC) during fall/winter to induce cessation of growth; dry weather enhances the quiescence and flower induction

• Warm (upper 60oF;20oC) temperatures late winter/early spring to induce flower initiation (flowering) and “good” fruit set; nonlimiting soil moisture

• High temperatures (>upper 60oF;20oC to upper 80oF;30oC) during fruit development and nonlimiting soil moisture

Production strategy for pummelo

• Time N fertilizer applications to support flowering and fruit development and postharvest A and carbohydrate accumulation

• Not to over apply N which results in favoring vegetative over reproductive growth

• Maintain all other nutrients at nonlimiting levels

• Maintain nonlimiting soil moisture from flowering through harvest

• Appropriate tree size control program to maintain productive canopy

• Maintain postharvest canopy for A and carbohydrate accumulation

Estimated plant nutrition

• Moderate soil fertility• Apply 100-200 lbs N acre-1

yr-1 (112-224 kg ha-1 yr-1)• Split nitrogen

applications into 2-4 application per year; prior or at bloom, mid-season, at or just after harvest

• Avoid excessive N applications during during fruit development period

• Secondary and minor elements should be applied on an as needed basis or maintenance level to maintain tree health

• Mg and Fe deficiencies are common during winter months due to reduced uptake under cool conditions. Apply foliar MgNO3 or MgSO4 and chelated iron prior to winter or to correct deficiencies

Range for mature trees Element Symbol Unit Lime Citrus Nitrogen N % 2.4 2.5-2.7 Phosphorus P % 0.25 0.12-0.16 Potassium K % 1.5 1.2-1.7 Calcium Ca % no data 3.0-4.9 Magnesium Mg % 0.18 0.30-0.49 Sulfur S % no data no data Boron B ppm no data 36-100 Iron Fe ppm no data 60-120 Manganese Mn ppm no data 25-100 Zinc Zn ppm no data 25-100 Copper Cu ppm no data 5-16 Molybdenum Mo ppm no data 0.10-1.0 Chlorine Cl % no data <0.2

Leaf nutrient levels??

Critical periods for irrigation

• At flowering and fruit set

• During fruit development

• During excessively drought conditions

• Irrigation rate (amount) varies with tree size, climatic demands, soil type and depth and should be determined with soil moisture monitoring

Tree training and tree size control

• Training of young trees, not common. However, heading back to force lateral development and removal of misplaced and V-crotched limbs will reduce problems later

• Trees size control may be by hand pruning and/or mechanical machinery (more common)

• Suggested tree size varies with environment, plant spacing, available technology, frequency of hurricanes, and cultivar growth habit and harvest season

• Reasons for tree size control – maintain light levels and lower productive canopy, improve crop production, increase air movement – reduce disease incidence, reduce potential hurricane damage

Tree training and tree size control

• In general, the warmer the climate the more vigorous tree growth is

• In general, pruning of large diameter stems/wood results in excessive/continuous vegetative flushing

• The wider the spacing the longer it takes to require regular pruning. The closer the plant spacing the earlier a pruning program is required and the more frequently trees are pruned

• In general, designing a pruning program for cultivars with a vigorous, upright growth habit is more difficult than for less vigorous, spreading growth habit cultivars

Tree training and tree size control

• Recommendation in Florida varies with cropping objectives

• Not known “best” time to prune since “normal” cropping season is summer/fall-winter

• Topping to open up the inner canopy to increase light penetration will help maintain lower productive canopy, and improve air movement to reduce fruit/leaf disease problems

• An indication of maturity is an increase in peel sheen, oil glands in the skin become more prominent starting near the tip of the fruit, progressing towards the stem end

Harvest indices

Pummelo crop production in Florida

Off-shore reported

8-9 tons/acre

Florida industry average at 10 years of tree age

• 15-20 tons/acre

Estimated annual cost of production ranges from $1,500-2,500 per acre

Estimated gross return is $0.40/packed lb

Major problems for pummelo crop production outside

Miami-Dade County, Florida

• Freezing temperatures that damage and/or kill potential fruiting stems

• Highly susceptible to citrus canker• Little experience with pummelo outside Miami-

Dade County• Many unknowns on how significant

insect/disease pressure would be

Major insects and diseases

• Scab (Elsinoe fawcetti)

• Greasy spot (Mycosphaerella citri)

• Melanose (Diaporthe citri)

• Algal disease (Cephaleuros virescens)

• Phytophthora root rot (P. parasitica and P. citrophthora)

• Postbloom fruit drop (P. acutatum)

• Broad mite (Polyphagotarsonemus latus)

• Rust mite (Phyllocoptuta oleivora)

• Citrus leaf miner (Phyllocnistis citrella)

• Various scales – Snow scale (Unaspis citri)

Postharvest handling

• Pick carefully and place bins in shade immediately

• Cool fruit to 55oF (12.5oC)• If available hydrocool or force-air cool• Sort and pack and place in cold storage

immediately• Optimum storage temperature is 45-48oF (7.2-

8.9oC), 85-90% RH; 12 wks

Environmental stress and management

• Drought – leaf wilting and cupping, chlorosis, desiccation, and abscission; fruit drop, reduced fruit size; stem and limb dieback; reduced crop yields; tree death

• Solutions - wide plant spacing, use of rootstocks for deeper rooting, mulching, irrigation

• Flood – leaf wilting and cupping, chlorosis, desiccation, and abscission; fruit desiccation and abscission; stem and limb dieback; severe crop loss; tree death

• Solutions – site selection, tolerant rootstocks, mounding, bedding, ditch/canal/ contour, subsurface drainage, hardpan disruption

Moderate tolerance Rootstock dependent

Environmental stress and management

• Freezing – leaf wilting, water soaking, desiccation, abscission; stem and limb dieback; fruit drop; tree death

• Solutions – site selection, high volume irrigation, wind machines

• Salinity – marginal and tip necrosis on leaves; stem and limb dieback; reduced fruit size, fruit drop; tree death

• Solutions – site selection, water quality and quantity – flushing soil profile periodically; tolerant rootstocks

Intolerant Rootstock influenced

Environmental stress and management

• Wind – stem and limb breakage; toppling, windthrow, stumping; tree death

• Solutions – site selection, wind breaks; rootstocks to facilitate deeper rooting for improved root anchoring; regular pruning program

• High pH, calcareous soil – nutrient deficiencies, especially iron, zinc, manganese, and magnesium

• Solutions – rootstock, frequent foliar applications of minor elements (Zn, Mn, Mg) and chelated Fe materials

Tolerant to intolerant Rootstock dependent

Credits

• Author – Dr. Jonathan H. Crane, Tropical Fruit Crops Specialist

• Photographs – copyrighted– Jonathan H. Crane

• This presentation is copyrighted, 2005 University of Florida, Institute of Food and Agricultural Sciences