US-812 (SxB)

Origin US-812 rootstock is a hybrid of Sunki mandarin and Benecke trifoliate orange (Citrus reticulata x Poncirus trifoliata) and was developed at the USDA in Fort Pierce, Florida, and has been commercially available since 2001. Ownership Open. General Description US-812 performs well on most replant soils in the citrus producing regions of South Africa, developing medium sized trees and good quality fruit on the young trees with good to excellent internal quality. However, US-812 is still relatively new in South Africa and has not been extensively tested with different cultivars under different soil conditions. Tree Characteristics Sweet orange trees on US-812 rootstock are large in field trials at Fort Pierce and in the Foundation planting in Winter Haven, Florida. The average tree size is similar to Carrizo citrange (medium to large), except for Star Ruby with a compact tree size similar to or smaller than C-35. Soil Type US-812 was selected as a rootstock option because of its tolerance to high pH and calcareous soils and generally performs well in most replant conditions.

Fruit Characteristics Fruit size on Midknight Valencia peaked at count 88, followed by counts 56 and 72. Delta Valencia in combination with US-812 peaked at counts 105/125, followed by counts 88 and 72. Production Trials are still relatively recent, but early yields have been good to excellent. Delta and Midknight Valencia trials were planted on US-812 in the Malelane area and produced an average crop of over a 100 kg per tree. Cultivar Options

US-812 is a promising new rootstock which can be

used on a semi- scale in combination with

grapefruit, Valencias, Navels and mandarins. Trials

indicate compatibility with Eureka lemon. General Initial tests suggest that this rootstock is resistant to Phytophthora, burrowing nematode and Citrus tristeza

virus (CTV). US-812 was included in a Delta Valencia trial with 42 different rootstocks and outperformed most of them (one of the top five rootstocks). Summary The main advantages of US-812 are: Phytophthora root rot resistant, nematode, CTV and blight tolerance, good internal quality fruit, precocious bearing, medium tree size, performs well on higher pH soils, and compatible with Eureka lemon.

Typical US-812 rootstock seed-source tree.

Updated: Sept 2021

Copyrights © 2021 Citrus Research International (Pty) Ltd. Reg. No. 2001/007745/07 All rights reserved. No part of this publication may

be reproduced, photocopied, stored on a retrieval system, or transmitted without the express written consent of the represented parties.

Disclaimer: Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought.

Sunki 812 (US 812) US-812 (S x B)

General Comments US-812 developed into a medium tree size in

combination with sweet oranges, mandarins and lemons, but with Star Ruby the tree size was smaller than C-35 (Star Ruby tree planted in 2000, only 3 m in height).

US-812 performs well on most replant soils and

conditions. Trials indicate that US-812 is tolerant to high pH and

calcareous soils. US-812 is resistant to Phytophthora and tolerant to

nematodes, CTV and blight, but is expected to be sensitive to citrus exocortis.

A rootstock trial located in the Letsitele area where

Gusocora Valencia was budded onto rough lemon, X639 and US-812 (trial 5 years old), US-812 outperformed the other two rootstocks with better yield on the young trees (precocious).

• US-812 in combination with Star Ruby grapefruit

developed a fairly small tree size in both the Northern Cape (Kakamas) and Malelane areas (Esselen nursery) in CRI trial blocks.

Delta Valencia planted on US-812 in 1999 with smooth bud-union and height of 3.5m.

Midknight Valencia planted on US-812 in 1999 with a tree height of 3.5 m.

Star Ruby grapefruit planted on US-812 in 2000 measuring 3.2m in size.

Copyrights © 2021 Citrus Research International (Pty) Ltd. Reg. No. 2001/007745/07 All rights reserved. No part of this publication may

be reproduced, photocopied, stored on a retrieval system, or transmitted without the express written consent of the represented parties.

Disclaimer: Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought.