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Evaluation of rootstocks for abiotic stress tolerance

: ZHU Shiping 1 2, LIU Xiaona1 2, LI Qingping3, YANG Yifei3, ZHAO Xiaochun1 2

: (1Citrus Research Institute, Southwest University/Chinese Academy of Agricultural Sciences,Chongqing 400712; 2National Citrus Engineering Research Center, Chongqing 400712; 3College of Horticulture and Landscape Architecture, Southwest University, Chongqing, 400715; China)

Email: wuhoujiu@cric.cn

Citrus is one of the most important fruit crops in the world, also in China. Citrus is distributed in most of regions in south China, mainly planted in the mountainous and hilly areas. The acidity, alkaline and drought are the most common abiotic stresses affecting the yield and quality of citrus. Selection and breeding of rootstock for those abiotic stresses are important for the citrus industry.

However, evaluation of abiotic stress tolerance in the field conditions is very difficult. It is not an easy task to maintain the physical and chemical properties of the soil to provide uniform conditions in large scale to assess the rootstocks for a long period of time. In this study, we developed a hydroponics based system in glasshouse to enable evaluation of large number of rootstock seedlings for abiotic stress tolerance. Several kind of rootstocks including Poncirus trifoliata Raf., Citrus junos Siebold.ex Tanaka, C. limonia Osbeck, C. reticulata Blanco, C. depressa Hayata, C. daoxinensis S.W.He, C. aurantium L., C. sinensis × P. trifoliata and Poncirus hybrid were investigated for the tolerances to acidity, alkaline and drought stresses.

  1. Acidity and alkalinity tolerances

The 6 month old seedlings were grown in hydroponics at pH6.5 for 60 days prior to treatment. The conditions used for acidity and alkaline treatments are pH3.5 and pH9.0, with the pH6.5 as control. The level of tolerance was evaluated by investigation of the symptom of leaf, and the physiological and biochemical parameters associated with stress tolerance such as MDA (malondialdehyde), soluble protein, Pro (proline), SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) were measured. Clustering and comprehensive subordinate function analysis indicated that the results of symptom observation were consistent with those of physiological and biochemical parameters analysis. The Shantousuanju (C. aurantium), Shiikuwasha and Ni 8047 (C. junos) showed great tolerance to low pH (pH3.5) stress, while Daoxianyeju (C. daoxinensis) and Nieduyeju (C. reticulate) were susceptible. Zhuju (C. reticulate), ‘Goutou’ sour orange (C. aurantium)and Shiikuwasha (C. depressa) possessed good adaptability to alkaline condition, while Daoxianensis and Nieduyeju were sensitive. Shiikuwasha demonstrated better tolerance to both high and low pH stresses.

 

  1. Drought tolerance

The seedlings of ten different rootstocks were used for water stress treatment under controlled conditions. Fully developed leaves from both controls and treatments were collected at the periods of 5, 10, 15 and 25 days after treatment for determination of the contents of malondialdehyde (MDA), proline and soluble protein, and also the activities of superoxide diamutase (SOD), catalase (CAT) and peroxidase (POD) to analyze the biochemical characteristics related to the stress tolerance. The morphological performances were investigated to assess the hazard index of the drought stress.

There were significantly difference on both time course and the severity of leaf wilting under water stress among the different varieties. Hongningmeng (C. limonia) began to wilt within ten days with hazard index of 16.6%, and at the 50th day after treatment, the hazard index raised up to 100%. Leaves of Ziyangxiangcheng (C. junos) and Shiikuwasha (C. depressa) showed symptom of wilt on 60th day; Z-021 (P. trifoliata) wilted on 70th, and its hazard index was 10%. Other trifoliate oranges and their hybrids did not wilt until 70th day of treatment. The drought tolerance of 10 citrus rootstocks were significantly different. The trifoliate hybrid ZZ-022 (Poncirus hybrid) was the most tolerant variety, while the mandarin Shiikuwasha was the most susceptible.

The difference on the changes of biochemical parameters between the control and treatment, among the different testing materials were quite obvious. The trends of change on the contents of proline, malondialdehyde and soluble protein varied among different rootstocks. The results of variance analysis showed that MDA content was obviously different among different periods of treatment (P<0.05). The content of soluble protein increased first and then decreased except that in XC-009 (C. junos). The contents of proline in all of 10 rootstocks demonstrated rising trend. Basically, the trends of change on SOD activity among the rootstocks were similar, which increased at early stage and decreased at late stage, and reached the maximum level on 15th day. However, the ranges of change varied among different rootstocks, POD activity in Z-006 (Poncirus hybrid) and Ziyangxiangcheng remained stable, but changed dramatically in XC-009. The activity of CAT in the most of rootstocks rose firstly and then declined. It reached to the peak on 5th day except in Hongningmeng. The results of comprehensive membership function and principal component analysis of biochemical parameters demonstrated a significant correlation with hazard index, particularly the PRO and SSC were highly associated with the drought tolerance.

 

nursery management approaches

: Jose Lima

: Wonderful Citrus

This presentation will cover a variety nursery management approaches to achieve quality trees for commercial plantings in one year or less,  small nursery trials and management strategies accumulated over the past three years will be shared including bud push techniques, inarching and others.

 

New Cultivars and the Challenge on the Obtention, Distribution and Commercialization.

: Luis Fernandez, Verena Müller, Veronica Herrera*

: ANA (Andes New Varieties Administration & Estación Experimental La Palma – Pontificia Universidad Católica de Valparaiso).

The new varieties are an aspect of fruit production of high interest for the industry, and therefore to the nurseries. In the past few decades, there have been changes in the legal frames, that determine the nature of the product development and modify the way and focus of the different actors in the development chain of new cultivars, including the nurseries.
Also, the increasing commercial exchange between countries, determine the need to improve the understanding  of the development of new varieties and the nursery role in these new scenarios.
The purpose of this lecture is to give a historical vision of the development of new varieties, the role of the different actors that arise in response to these changes  and a brief summary of the commercial models in which new varieties are developed, including the experience in other fruit species.

Nursery Production Farm Management System

: John McDonald

: 1National Biosecurity Manager Nursery & Garden Industry Australia

Email: john.mcdonald@ngia.com.au

The Australian nursery industry has developed an industry specific Farm Management System (FMS) that includes three key programs designed for nursery production addressing best management practice, environmental management and on-farm biosecurity, all independently audited on an annual cycle.  NIASA (Nursery Industry Accreditation Scheme Australia) Best Management Practice is the cornerstone of the Nursery Production FMS. For a professional business to remain at the forefront of their industry it is paramount they adopt industry best management practices and assess their change management.  EcoHort™ (Nursery Industry Environmental Management System) is integrated into the Nursery Production FMS through the EcoHort™ Guidelines which provide a risk assessment based pathway for a business to demonstrate their sound environmental stewardship and natural resource management. BioSecure HACCP (On-farm Biosecurity Program) is the industry biosecurity program under the Nursery Production FMS. This program seeks to identify internal and external threats/risks to biosecurity within an individual business and implement critical control points against these risks to manage impacts. BioSecure HACCP is a set of protocols and procedures that enable a business to manage biosecurity risks establishing an effective internal quarantine process for both imported and exported plant material.

Dynamic growth in South African citrus industry – coping with the demand for propagation material

: Paul Fourie, Jacolene Meyer, Thys du Toit and Michelle le Roux

: Southern African Citrus Improvement Scheme, Citrus Research International (Pty) Ltd,

The objective of the southern African Citrus Improvement Scheme (SACIS) is to increase the profitability of the southern African Citrus Industry by ensuring that growers are supplied with nursery trees of the highest possible quality made from the best genetic citrus material and being free from any harmful pathogens. The SACIS is operated from the Citrus Foundation Block (CFB) biosecure multiplication facility, which supplies >80% of rootstock seed and >95% of citrus budwood to nurseries and growers in Southern Africa. For many years, seasonal budwood supply ranged between 2.5 and 3.2 million buds per season, but over the last 4 years budwood demand has steadily increased to ≈6.5 million buds supplied in 2016/17. Likewise, tree capacity in nurseries has doubled over the past few years, and several new nurseries were SACIS certified. Of the >350 cultivars maintained and multiplied at CFB, 67% is protected and privately managed cultivars. Apart from the active marketing of these protected cultivars, budwood supply dynamics are influenced by the rapid changes in demand for cultivars dependent on the success or failures of cultivars in overseas markets. Concomitant stock and multiplication planning required good market intelligence and a “crystal ball”. Unprecedented demand for lemon and late mandarin cultivars has outstripped supply from CFB, which necessitated authorization of budwood cutting from certifiable sources in nurseries, as a certified secondary supply source. Record growth and urgent demand for highly sought after new varieties have strained resources and new rapid multiplication strategies will have to be implemented to supply the demand.

Production of Citrus Trees in Greenhouses

 

A green thumb isn’t enough. To succeed in today’s competitive nursery industry, a grower must have a basic understanding of plant growth and know how to manage the greenhouse environment to maximize tree growth and profits.

There is a lot of information on the different types of greenhouses available today on the market. My goal today is not to discuss different greenhouse structures but to focus on the advantages of growing trees in a greenhouse vs a screenhouse environment and to provide some basic parameters for optimal tree growth.

The advantage of growing the trees in a greenhouse is that plant environment can be controlled to the specific plant requirements. Most ornamental crops grown in greenhouses today, have detailed notes on how to produce them. These crop notes include information on propagation, media, temperature, light levels, humidity, nutrition, etc. but when it comes to growing citrus in a greenhouse there is very little information available.

I would like to share some of the things that we have learned in the last four years of growing trees in a greenhouse and some of the parameters we are using to maximize plant growth.

  • Discuss advantages and disadvantages of growing trees in a greenhouse vs screenhouse
  • CO2 levels
  • Light levels
  • Temperature and humidity
  • Soil moisture
  • Greenhouse conditional controls

 

Rootstock Effects on Substrate pH

: Nate H. Jameson

: Brite Leaf Citrus Nursery, LLC