First report of Cuscuta sp. in Eucalyptus clonal propagation

The genus Cuscuta L. consists of parasitic plants, also referred to as holoparasitic plants; the Family Convolvulacae includes 219 species distributed around the world, except in Antarctica and Greenland (⁷). In Brazil, 26 species are known to occur in all biomes and types of vegetation (⁴). Cuscuta species have been reported to exert a negative effect on the vegetative and reproductive development of Zornia diphylla, a native Caatinga plant (²), and to cause economic losses to crops of tomato, pepper, potato, carrot, onion, beet, tobacco, coffee, citrus, and crown of thorns (⁶). During routine sanitary inspections in 2018, a parasitic plant was found on a eucalypt clone (Eucalyptus urophylla var. platyphylla) in a clonal seedling nursery in Monsenhor Gil, Piauí State, Brazil, where average annual temperature is 26.6 ºC, annual rainfall is 1400 mm, and Köppen climate type is Aw (¹). The parasitic plant was identified as Cuscuta sp., based on morphological characteristics. In 2019, eucalypt mini-stumps parasitized with Cuscuta sp. were observed in another clonal nursery located in Dom Eliseu, Pará State, Brazil, where average annual temperature is 27.1 ºC, annual rainfall is 1900 mm, and climate type is Am (¹). Based on the history of the mini-garden in Dom Eliseu, it had been recently formed with clonal eucalypt seedlings originated from the nursery in Monsenhor Gil. Therefore, it is plausible that there has been an unintentional dissemination of Cuscuta sp. between the nurseries (Figure 1 A-C). Preliminary histological analysis of healthy stems and mini-stumps attacked by Cuscuta sp. (Figure 1 D-K) allowed a qualitative approach of this interaction. There is a reduction in xylem tissue attributed to colonization by Cuscuta sp. endophyte. Additionally, the cambium activity is so much hampered that as soon as the endophyte reaches and colonizes the cambium region, no more vascular cells are produced in the infected stem section (Figure 1 J-K). This preliminary approach leads to the hypothesis that attacked eucalypt mini-stumps will show reduced number and diameter of vessel elements, which may imply decreased productivity in cutting production since the sap movement will be impaired. Furthermore, commercialization or exchange of clonal eucalypt seedlings from contaminated nurseries represents a high risk of spreading the parasitic plant, which was also commented by Ferreira (³) for infected ornamental seedlings. Another potential risk is the spread of diseases, since Cuscuta sp. is an important vector, especially of phytoplasms and viruses (³, ⁵). A single citation of the presence of Cuscuta sp. in seminal E. grandis seedlings was found for the region of Santa Maria in Rio Grande do Sul State (⁸). Thus, the present study is the first report of Cuscuta sp. in a clonal nursery of eucalypt seedlings in Brazil. Confirmation of this new invasive plant in nurseries implies the need for further studies specifically related to control strategies.

Figure 1
Interaction of Cuscuta sp. with Eucalyptus mini-stumps in the clonal mini-garden. A - Eucalypt mini-stumps in a clonal mini-garden planted in raised beds with sand substrate; B - Detail of the external morphology of the interaction between Cuscuta sp. and the mini-stumps; C - Detail of the contact point in the haustoria region of the parasitic plant (stars); D - Cross section of a healthy mini-stump; E - Longitudinal section of a healthy mini-stump; F - Cross section of a parasitized mini-stump between regions of haustoria penetration; G - Cross section of a parasitized mini-stump in the haustoria penetration region; H, I and J - Different longitudinal sections of parasitized mini-stumps showing the primordium of endophyte (arrows illustrate the orientation of the same structures in different cutting planes); K - Longitudinal section of a parasitized mini-stump indicating the distribution of the parasitic plant tissues in the cortical and phloemic region of the host plant (heads of smaller arrows). Heads of larger arrows indicate cambial region; rectangles show the same region in healthy (D) and parasitized (F) plants. Scale reference bars in subfigures D – K are equivalent to 200 µm.

ACKNOWLEDGEMENTS

The authors would like to thank Suzano S.A. for financial support and Amilton, Plantbem Nursery, for collaboration as well as for collection and delivery of the analyzed samples.

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Edited by

Editor associado para este artigo: Paulo César Ceresini

Publication Dates

• Publication in this collection
  28 Aug 2023
• Date of issue
  2023

History

• Received
  15 Oct 2022
• Accepted
  20 Apr 2023