Avocado rootstock named ‘Merensky 6’

Abstract

A new and distinct variety of Persea americana tree imparting high bearing capacity and vigor to the scion cultivar when used as a rootstock. Further, this rootstock exhibits a high tolerance to Phytophthora cinnamomi.

Claims

1. A new and distinct rootstock variety of avocado tree having the characteristics as described and illustrated herein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying photographs show specimens of the tree and plant parts of the new Merensky 6 variety.

(2) FIG. 1 is a photograph depicting a four-year-old, top-worked tree of the Merensky 6 variety while growing in Tzaneen, Limpopo Province, South Africa

(3) FIG. 2 is a photograph depicting typical mature foliage of the Merensky 6 variety, above a tape measure in centimeters for size reference;

(4) FIG. 3 is a photograph depicting typical flush foliage of the Merensky 6 variety, above a tape measure in centimeters for size reference;

(5) FIG. 4 is a photograph depicting typical inflorescence of the Merensky 6 variety, above a tape measure in centimeters for size reference;

(6) FIG. 5 is a photograph depicting a typical external view of the fruit of the Merensky 6 variety, above a tape measure in centimeters for size reference; and

(7) FIG. 6 is a photograph depicting typical internal views of the fruit of the Merensky 6 variety, with and without the seed, above a tape measure in centimeters for size reference.

DETAILED BOTANICAL DESCRIPTION OF THE VARIETY

(8) The following is a detailed description of the new Merensky 6 variety, which was taken from approximately 4-year-old mature trees, with the exception as a rootstock for a specific scion when reference is made to root rot tolerance and yield. The trees are located in an experimental orchard at Tzaneen, Limpopo Province, South Africa, and are grafted on a Merensky 2 rootstock.

(9) In those instances where precise color assessment could be made, The Royal Horticulture Society (R.H.S.) color numbering system (R.H.S. Colour Chart published by The Royal Horticultural Society, London 2001) is used herein for the color description of the rind, seed, bark, leaf, flower, flesh color and other characters of the Merensky 6 avocado tree. In other instances, generally, color terms are used in accordance with an ordinary dictionary significance.

(10) With reference now to FIG. 1, the Merensky 6 tree has an upright and vigorous growth habit. Below in Table 1 are data on the vigor of Hass grafted onto the rootstock of Merensky 6 as determined by trunk diameter measurements, taken 20 cm from the soil line, from trees planted in an orchard with Phytophthora cinnamomi in Tzaneen, Limpopo Province, South Africa.

(11) TABLE-US-00001 TABLE 1 Trunk diameter (cm) Rootstock Year 2 Year 3 Year 4 Year 5 Year 6 Merensky 6 7.1 1.1 8.6 1.4 11.4 1.7 13.7 2.0 16.2 2.2 Duke 7 5.6 1.0 6.5 1.1 8.2 1.3 9.3 1.5 10.8 1.7 Tzaneen, Limpopo Province, South Africa, with Hass scion (n = 24)

(12) Below are data on the vigor of Hass grafted onto the rootstock of Merensky 6 as determined by trunk diameter measurements, taken 5 cm from the soil line, from trees planted in an orchard with Phytophthora cinnamomi in Goleta, Calif., USA.

(13) TABLE-US-00002 TABLE 2 Trunk diameter (cm) Rootstock Year 2 Year 3 Year 4 Merensky 6 6.1 3.8 9.4 0.7 11.2 1.0 Merensky 2 6.8 3.1 8.4 2.7 11.4 1.2 Goleta, California, USA, with Hass scion (n = 15)

(14) Table 3 below provides the data on the typical canopy size of Hass grafted onto the rootstock of Merensky 6 as determined by canopy volume measurements from trees planted in an orchard with negligible Phytophthora cinnamomi and salinity levels in Goleta, Calif., USA.

(15) TABLE-US-00003 TABLE 3 Canopy volume (m.sup.3) Rootstock Year 2 Year 3 Year 4 Merensky 6 9.2 2.2 11.1 2.3 15.2 1.1 Merensky 2 7.7 3.0 10.5 2.9 17.0 1.9 Goleta, California, USA, with Hass scion (n = 15)

(16) With reference now to FIGS. 2-4, the color of a one-year-old branch of Merensky 6 is yellow-green (RHS 146B). The bark of the one-year-old old branch is smooth. The lenticels of the one-year-old branch are inconspicuous.

(17) The color of the main stem is grey-brown (RHS 199A). The texture of the bark of the main stem is corky.

(18) The young shoot (flush) has a very weak intensity of anthocyanin coloration. The color of the young shoot is yellow-green (RHS 146A). The conspicuousness of lenticels is high. The lenticels of the young shoot are greyed-purple (RHS 185B). By comparison, lenticels of Duke 7 are green (RHS 139B). The size of the lenticels of the young shoot of the Merensky 6 is approximately 1.0 mm long. There are approximately +/20 lenticels per square cm. The color of the upper side of the young shoot is yellow-green (RHS 146A). The upper side of the young shoot has high glossiness. The lower surface of the young shoot has a yellow-green (RHS 146B) color.

(19) A mature leaf of the Merensky 6 variety has a length of approximately 19.0 cm and a width of approximately 6.0 cm, for a length/width ratio of 3.2. The shape of the mature leaf is lanceolate. The color of the upper side of the mature leaf is green (RHS 137A), and has a medium glossiness. The lower side of a mature leaf of the Merensky 6 leaf is green (RHS N138C). Veins are prominent and in relief on the lower side of the mature leaf. The color of the veins is yellow-green (RHS 151A). The mature leaves have a generally flat shape and cross-section. The color of the petiole of a mature leaf is yellow-green (RHS 144C). The length of the leaf petiole is approximately 3.7 cm. The mature leaf has a medium anise aroma. The margin of the mature leaf has a weak undulation. Reflexing of apex is present. The mature leaf apex shape and base shape are both acute. The leaves are held horizontally, i.e., approximately perpendicular to the shoot.

(20) The bud shape of the Merensky 6 flower is ovoid. The bud size is approximately 5 mm in length and approximately 4 mm in diameter. The bud color is yellow-green (RHS 145A). The flower belongs to Group A, with female opening occurring in the morning and ending before noon. The male opening occurs in the afternoon of the next day. The flower's opening cycle lasts approximately 30-36 hours. The petals of the flower are borne in two whorls of three perianth lobes. The petals possess entire margins and petal coloration is yellow-green (RHS 145C). There are commonly nine fertile stamens, each having two basal orange nectar glands and three staminodia. The anthers are tetrathecal. The single pistil with a slender style and small stigmatic surface has one carpel with one ovule. The ovary is superior. The pedicel is commonly approximately 2.3 mm in length and approximately 1.2 mm in diameter. The coloration of the pedicel is yellow-green (RHS 145A). There are approximately 60-80 flowers per inflorescence. Generally, Merensky 6 has been found to bloom in July at Tzaneen, Limpopo Province, South Africa. The flowering time in California, USA, has been found to be between March and April.

(21) The fruit of the Merensky 6 has a length of approximately 8.7 cm and a width of approximately 5.6 cm, for a ratio length/width of 1.6. The shape of the fruit is ellipsoid. The color of the skin of the fruit, when ripe, is yellow-green (RHS 146A). The texture of the skin of the fruit is smooth. Longitudinal ridges are absent. The thickness of the skin of the fruit is moderately thin. There is an intermediate adherence of the skin to the flesh of the fruit. The main color of the flesh is yellow-green (RHS 154C). The color of the intensely colored area of flesh next to the skin is yellow-green (RHS 144A). The width of the intensely colored area of flesh next to the skin is approximately 3.0 mm. Fibers in the flesh are conspicuous.

(22) The seed of the Merensky 6 has a length of approximately 5.1 cm and a width of approximately 3.6 cm, on average. The shape, in longitudinal section, is ovate, and circular in cross-section. The color of the seed coat (fresh) is greyed-orange (RHS 166B).

(23) The Merensky 6 fruit ripen in February in Tzaneen, Limpopo Province, South Africa; and in September in California, USA. The fruit of Merensky 6 are not intended for market use. Instead, the variety is intended to be used as a vegetatively propagated rootstock onto which commercial varieties such as Hass, are grafted.

(24) Table 4 through Table 8 provide data on the yield of the Merensky 6 rootstock as compared to other rootstocks, for various scions and locations in South Africa and California. The data from these tables, taken from field trials, show that the Merensky 6 rootstock imparts a high bearing capacity to the scion.

(25) TABLE-US-00004 TABLE 4 Yield (kg/tree) Rootstock Year 2 Year 3 Year 4 Merensky 6 0.3 0.5 4.6 5.3 0 Duke 7 0.3 0.6 1.2 1.1 0 Yield (kg/tree) Rootstock Year 5 Year 6 Cumulative Merensky 6 40.7 12.4 38.0 19.3 83.6 28.6 Duke 7 16.9 10.3 6.3 11.8 24.7 17.5 Tzaneen, Limpopo Province, South Africa, with Hass scion (n = 24)

(26) TABLE-US-00005 TABLE 5 Yield (kg/tree) Rootstock Year 2 Year 3 Year 4 Year 5 Merensky 6 19.7 10.3 46.8 19.6 16.3 9.0 73.3 24.1 Merensky 2 13.4 10.5 42.2 14.6 19.9 12.0 59.8 24.1 Yield (kg/tree) Rootstock Year 6 Year 7 Year 8 Cumulative Merensky 6 18.9 21.8 34.7 19.4 117.9 27.6 327.6 83.9 Merensky 2 21.9 23.5 21.8 21.2 78.5 18.6 257.5 77.1 Morebeng, Limpopo Province, South Africa, with 3-29-5 scion (n = 45)

(27) TABLE-US-00006 TABLE 6 Yield (kg/tree) Rootstock Year 2 Year 3 Year 4 Year 5 Merensky 6 31.3 7.4 17.5 18.6 48.7 22.5 74.1 26.9 Merensky 2 23.5 9.0 19.0 15.9 34.9 18.3 50.6 26.1 Yield (kg/tree) Rootstock Year 6 Year 7 Year 8 Cumulative Merensky 6 72.8 47.3 26.2 35.0 157.0 47.2 427.6 87.3 Merensky 2 26.3 25.4 23.3 20.0 107.0 41.1 284.6 88.5 Morebeng, Limpopo Province, South Africa, with Hass scion (n = 45)

(28) TABLE-US-00007 TABLE 7 Yield (kg/tree) Rootstock Year 2 Year 3 Year 4 Merensky 6 22.4 10.6 12.6 14.0 19.5 11.7 Merensky 2 14.9 11.5 12.2 11.4 16.4 13.9 Yield (kg/tree) Rootstock Year 5 Year 6 Cumulative Merensky 6 11.9 11.3 15.6 15.7 81.9 21.4 Merensky 2 7.4 9.5 8.9 10.1 59.8 31.0 Santa Paula, California, USA, with Hass scion (n = 10)

(29) TABLE-US-00008 TABLE 8 Yield (kg/tree) Rootstock Year 2 Year 3 Year 4 Cumulative Merensky 6 8.3 5.5 23.0 14.1 14.0 14.1 45.3 17.1 Merensky 2 4.2 5.3 23.7 10.0 14.0 9.5 41.8 16.5 Goleta, California, USA, with Hass scion (n = 15)

(30) As shown in Table 9 and Table 10 below, which represent data of tree health of the Hass scion on Merensky 6 as compared to using Merensky 2, Hass trees on the Merensky 6 rootstock are healthier than those on the Merensky 2 rootstock.

(31) TABLE-US-00009 TABLE 9 Tree Health Rootstock (0-10; 10 = Dead) Merensky 6 0.1 0.3 Merensky 2 3.2 0.8 Santa Paula, California, USA, with Hass scion, 6-year-old trees (n = 10)

(32) TABLE-US-00010 TABLE 10 Tree Health Rootstock (0-10; 10 = Dead) Merensky 6 1.1 1.8 Merensky 2 1.9 3.6 Goleta, California, USA, with Hass scion, 4-year-old trees (n = 15)

(33) The Merensky 6 variety and rootstock have shown a strong tolerance to Phytophthora cinnamomi.