A dark incubation period is important for Agrobacterium-mediated transformation of mature internode explants of sweet orange, grapefruit, citron, and a citrange rootstock.

Mizuri Marutani-Hert,Randall P Niedz,Terence J Evens,T Erik Mirkov,Kim D Bowman,Greg T Mccollum

doi:10.1371/journal.pone.0047426

Mizuri Marutani-Hert, Randall P Niedz + Show 4 more

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https://doi.org/10.1371/journal.pone.0047426

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Abstract

BackgroundCitrus has an extended juvenile phase and trees can take 2–20 years to transition to the adult reproductive phase and produce fruit. For citrus variety development this substantially prolongs the time before adult traits, such as fruit yield and quality, can be evaluated. Methods to transform tissue from mature citrus trees would shorten the evaluation period via the direct production of adult phase transgenic citrus trees.Methodology/Principal FindingsFactors important for promoting shoot regeneration from internode explants from adult phase citrus trees were identified and included a dark incubation period and the use of the cytokinin zeatin riboside. Transgenic trees were produced from four citrus types including sweet orange, citron, grapefruit, and a trifoliate hybrid using the identified factors and factor settings.SignificanceThe critical importance of a dark incubation period for shoot regeneration was established. These results confirm previous reports on the feasibility of transforming mature tissue from sweet orange and are the first to document the transformation of mature tissue from grapefruit, citron, and a trifoliate hybrid.

Highlights

Citrus is grown worldwide, is consumed both fresh and processed, and is one of the most economically important fruit crops
The shoot induction medium (SIM) medium used was based on results from prior experimentation that determined the effects of various cytokinins and auxins on shoot regeneration from juvenile epicotyl explants of sweet orange and grapefruit [33]
An analysis of variance (ANOVA) was conducted for each citrus type and showed that the effect of a dark incubation period on the number of shoots regenerated was significant (Table 2); the means 6 S.D. are shown in Table 2 and Figure 3

Summary

Introduction

Citrus is grown worldwide, is consumed both fresh and processed, and is one of the most economically important fruit crops. One of the reasons for the long development time is an extended juvenile phase in citrus that typically requires at least 5–10 years before flowering Another reason is that a new selection is tested at multiple field locations, with multiple rootstocks or scions, and over at least four years of fruit production to provide an estimate of productivity. There are some serious barriers in citrus biology that must be overcome before progress can be made, and include: the difficulties and expense of working with a tree crop, a long juvenile phase, and many citrus exhibit apomixis and inbreeding depression. These barriers, taken together, make citrus one of the most difficult crops to breed. Methods to transform tissue from mature citrus trees would shorten the evaluation period via the direct production of adult phase transgenic citrus trees

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