The Irwin variety originated in Florida, United States, in 1949 as an open pollinated seedling of Lippens. The variety was introduced into Australia in the late 1970s as part of the department´s mango introduction and evaluation program.
Irwin is a monoembryonic* variety, grown commercially in many regions of Australia. Although Irwin is no longer a commercial variety it produces consistent high yields in the northern and southern growing regions where Kensington Pride is less reliable.
Irwin is a medium-sized tree, with a semi-open canopy and slightly spreading branch habit. Six-year-old trees are typically 5 m high with a canopy diameter of 4 m.
- panicle* length - 30-35 cm
- panicle width - 20 cm
- hair density - few
- panicle colour - purple
- wilted petals - red/pink.
- fruit shape - ovate
- Ground colour - yellow
- blush colour - red
- weight - 262 g
- average length - 92 mm
- average width - 63 mm
- average depth - 67 mm
- lenticel size - small
- lenticel colour - yellow
- pulp colour - yellow
- firmness - medium to soft
- stem end shape - level
- beak shape - slight
- pulp recovery - 64 per cent
- flavour - sweet mild
- embryo type - monoembryonic*.
Irwin is a monoembryonic variety, which means that the seeds, if planted, will not produce seedlings that fruit true to type. For this reason, Irwin has to be propagated vegetatively and grafting is the preferred method. In Australia, Kensington Pride is the most commonly used rootstock.
Planting densities for Irwin are generally higher than for Kensington Pride and R2E2. Irwin is best planted 4-6 m between trees and 7-9 m between rows (185-357 trees/ha).
Pruning and shaping
Irwin is not a vigorous variety and does not require excessive pruning. During the early years of growth, branches should be tipped twice yearly to maximise the number of fruiting terminals and produce well-branched limbs that maximise the number of bearing terminals. Bearing trees require an annual post-harvest pruning to thin the outer canopy and remove any branches deformed by heavy crop loads. Skirting up to a height of about 1 m will allow machinery access under the canopy.
Irwin is a consistently heavy cropping variety in most growing regions. It does not usually suffer from the annual yield fluctuations that Kensington Pride does, particularly in the tropical northern regions. An 8- to 9-year-old tree will yield approximately 100 kg of fruit. However, fruit size at maturity can be variable as Irwin can retain many nubbins that grow to only three-quarters of the size of seeded fruit. Irwin is a mid-season variety that matures after Kensington Pride and before Keitt.
Pest and disease status
Irwin is moderately to highly susceptible to bacterial black spot(Xanthomonas campestris pv. mangiferaeindicae) and anthracnose (Colletotrichum gloeosporioides). Stem end rots (Botryosphaeria spp. and Lasiodiplodia theobromae) will also affect Irwin.
Irwin is affected by major insect pests such as mango scale (Aulacaspis tubercularis), mango shoot caterpillar (Penicillaria jocosatrix) and tipborer (Chlumetia euthysticha), fruit flies and planthopper (Colgaroides acuminata).
Irwin can suffer from the internal fruit disorder known as jelly seed, which appears as a premature ripening of the fruit pulp around the seed. The sap of Irwin is not as caustic as Kensington Pride so sapburn is not generally a problem. When the fruit is ripe, the skin is very thin and easily damaged during handling.
Irwin should be harvested when hard mature, as the fruit is very soft when ripe and susceptible to damage during transport. Fruit size at maturity is often variable, as nubbins are often held full term.
Townsville, Burdekin and Bowen region
Pores in the skin of the fruit
Single embryo in seed, producing a seedling that is a genetic cross between the mother tree and pollen donor
Branched flower spike with many flowers
Seed with multiple embryos, producing seedlings that are genetically identical to parent tree