Orobanche crenata: A Bibliometric Analysis of a Noxious Parasitic Plant

Orobanche crenata is a parasitic weed representing a serious constraint to crop production in the Mediterranean basin. Here, we aim to evaluate the global scientific research status and trends of O. crenata through a bibliometric analysis to identify prominent research themes, development trends, and major contributors in terms of authors, institutions, countries, and journals. In the span of 53 years, from 1968 to 2021, 274 articles related to this field were retrieved from Scopus database and were analyzed using VOSviewer and BiblioShiny software. Results showed that 70.4% of all articles on O. crenata have been published in the last two decades. "Control methods" was the most prevalent research theme with 55.9% of all articles. Weed Research is the most influential journal. The countries with the highest number of articles were Spain, Egypt, and Italy. The Institute for Sustainable Agriculture is the most involved institution, contributing to 31.7% of all articles, and authors from Spain were the most productive. The latest research literature (5 years) was performed mainly by authors from Spain, Morocco, and Tunisia, emphasizing the persistence of this constraint in these countries. Keyword analysis revealed that "Vicia faba", "germination", and "legumes" are the most researched hotspots. Despite the growing collaborative behavior in this area, cooperation between countries is still deficient and should be extended to countries that are recently affected by this scourge to exchange expertise already acquired by experienced researchers, thus allowing better worldwide control of this parasitic weed.

A novel sunflower broomrape race with unusual virulence potentially caused by a mutation

Introduction

The sunflower broomrape (Orobanche cumana Wallr.) gene pools of the Guadalquivir Valley and Cuenca province in Spain had predominantly race-F virulence. A new race G was observed recently in the Guadalquivir Valley potentially due to the genetic recombination of the avirulence genes of both gene pools.

Methods

In this research, we have studied populations with atypical virulence from Cuenca. These populations parasitize on DEB2 sunflower line, resistant to all race-G populations evaluated. Ten populations collected in Cuenca province were evaluated with sunflower differential lines and genotyped with 67 SNP markers.

Results

Although genetic recombination with individuals of the Guadalquivir Valley gene pool has been observed in most populations, recombination of avirulence genes was discarded as the cause of the new virulence because the population with the highest degree of attack on DEB2 showed no introgression from an external gene pool. Accordingly, a point mutation is proposed as the putative cause of the new virulence.

Discussion

The present study provided a detailed characterization of each population, including the accurate classification of the individuals belonging to each of the classical Spanish gene pools, F1 hybrids, and those that evolved from hybridization between both gene pools. This information is essential to understand how sunflower broomrape populations are evolving in Spain, which in turn may be helpful to understand the dynamics of sunflower broomrape populations in other areas of the world and use this information to develop durable strategies for resistance breeding.

Wild Helianthus species: A reservoir of resistance genes for sustainable pyramidal resistance to broomrape in sunflower

Orobanche cumana Wall., sunflower broomrape, is one of the major pests for the sunflower crop. Breeding for resistant varieties in sunflower has been the most efficient method to control this parasitic weed. However, more virulent broomrape populations continuously emerge by overcoming genetic resistance. It is thus essential to identify new broomrape resistances acting at various stages of the interaction and combine them to improve resistance durability. In this study, 71 wild sunflowers and wild relatives accessions from 16 Helianthus species were screened in pots for their resistance to broomrape at the late emergence stage. From this initial screen, 18 accessions from 9 species showing resistance, were phenotyped at early stages of the interaction: the induction of broomrape seed germination by sunflower root exudates, the attachment to the host root and the development of tubercles in rhizotron assays. We showed that wild Helianthus accessions are an important source of resistance to the most virulent broomrape races, affecting various stages of the interaction: the inability to induce broomrape seed germination, the development of incompatible attachments or necrotic tubercles, and the arrest of emerged structure growth. Cytological studies of incompatible attachments showed that several cellular mechanisms were shared among resistant Helianthus species.

Correlational nutritional relationships and interactions between expansive holoparasite Orobanche laxissima and woody hosts on metal-rich soils

Plant parasitism by other plants, combined with abiotic environmental stress, offers a unique opportunity to study correlational nutritional relationships in terms of parasite-host interactions and their functional roles in nutrient cycling in ecosystems. Our study analysed the transfer of selected mineral elements, including heavy metals, from soil to different organs in hosts (Punica granatum and Fraxinus angustifolia) and from hosts to the expansive holoparasite (Orobanche laxissima) in cinnamonic soil habitats in Georgia (Caucasus). We also identified other correlated trophic and bioactive effects in the parasite-host relationship. O. laxissima was characterized by a high accumulation tendency for micro- and macroelements, such as K and Ca, and heavy metals, such as Zn, Ni, and Cd. Parasites can reduce the concentration of heavy metals in host tissues owing to this high accumulation tendency. In total, 85 compounds were identified in the examined parasite and its hosts. Despite the distinct phytochemical content of species of the infected host, the parasite produced specific metabolites with dominant phenylethanoid glycosides (PhGs), with acteoside and crenatoside being the primary dominant compounds - ca. 98% of all polyphenols. Polyphenols in parasite specimens that are correlated with Cu and Zn are antagonistic to polyphenols correlated with Fe, Pb, Cr, and Ni. The profile of polyphenols in the host species was both qualitatively and quantitatively distinct from the profile of the compounds in the parasite and between hosts (only acteoside in group PhGs was common between the parasite and Fraxinus host), which indicates the existence of a unique compound biosynthesis pathway in the parasite. Our results demonstrated that the parasite, particularly in its flowers, exhibited higher polyphenol content, antioxidative effects (ABTS-+, DPPH, and FRAP), and inhibitory effects.

Holoparasitic plant-host interactions and their impact on Mediterranean ecosystems

Although photosynthesis is essential to sustain life on Earth, not all plants use sunlight to synthesize nutrients from carbon dioxide and water. Holoparasitic plants, which are important in agricultural and natural ecosystems, are dependent on other plants for nutrients. Phytohormones are crucial in holoparasitic plant-host interactions, from seed germination to senescence, not only because they act as growth and developmental regulators, but also because of their central role in the regulation of host photosynthesis and source-sink relations between the host and the holoparasitic plant. Here, we compile and discuss current knowledge on the impact and ecophysiology of holoparasitic plants (such as the broomrapes Orobanche sp. and Phelipanche sp.) that infest economically important dicotyledonous crops in Mediterranean agroecosystems (legumes [Fabaceae], sunflowers [Helianthus sp.], or tomato [Solanum lycopersicum] plants). We also highlight the role of holoparasitic plant-host interactions (such as those between Cytinus hypocistis and various shrubs of the genus Cistus) in shaping natural Mediterranean ecosystems. The roles of phytohormones in controlling plant-host interactions, abiotic factors in parasitism, and the biological significance of natural seed banks and how dormancy and germination are regulated, will all be discussed. Holoparasitic plants are unique organisms; improving our understanding of their interaction with hosts as study models will help us to better manage parasitic plants, both in agricultural and natural ecosystems.

Aspergillus alliaceus infection fatally shifts Orobanche hormones and phenolic metabolism

In this study, the physio pathological effects of Aspergillus alliaceus (Aa, fungi, biocontrol agent) on Orobanche (parasitic plant) were investigated by hormone and phenolic substance tests. In experimental group, Orobanches were treated with the fungi, considering control group was fungus-free. Based on the hormonal tests, in the experimental group, salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA) and gibberellic acid (GA) levels significantly decreased, and only indole acetic acid (IAA) hormone levels were fairly higher than the control group. According to phenolic substance tests, it was found that only gallic acid, syringic acid and caffeic acid values significantly increased compared with control, and catechin and p-coumaric acid values were significantly lower. Consequently, it was determined that Aa pathogenesis (1) considerably reduces the effects of all defence hormones (JA, ABA, SA), (2) operates an inadequate defence based solely on the IAA hormone and several phenolic substances (gallic acid, syringic acid and caffeic acid), (3) and inevitably the fungi lead the Orobanche to a slow and continuous death. The results were evaluated in detail in the light of similar recent article and current literature in terms of biocontrol and pathology.

Genetic and Genomic Tools in Sunflower Breeding for Broomrape Resistance

Broomrape is a root parasitic plant causing yield losses in sunflower production. Since sunflower is an important oil crop, the development of broomrape-resistant hybrids is the prime breeding objective. Using conventional plant breeding methods, breeders have identified resistant genes and developed a number of hybrids resistant to broomrape, adapted to different growing regions worldwide. However, the spread of broomrape into new countries and the development of new and more virulent races have been noted intensively. Recent advances in sunflower genomics provide additional tools for plant breeders to improve resistance and find durable solutions for broomrape spread and virulence. This review describes the structure and distribution of new, virulent physiological broomrape races, sources of resistance for introduction into susceptible cultivated sunflower, qualitative and quantitative resistance genes along with gene pyramiding and marker assisted selection (MAS) strategies applied in the process of increasing sunflower resistance. In addition, it presents an overview of underutilized biotechnological tools, such as phenotyping, -omics, and genome editing techniques, which need to be introduced in the study of sunflower resistance to broomrape in order to achieve durable resistance.

Development of phloem connection between the parasitic plant Orobanche cumana and its host sunflower

Orobanche cumana is a root parasitic plant causing considerable yield losses in sunflower cultivation. The holoparasite fulfills its entire demand for water, minerals, and organic nutrients from the host's vascular system. In this study, the ultrastructure of the phloem connection between the haustorium of young O. cumana tubercles and the sunflower root has been examined for the first time. Parasite and host tissues were intermingled at the contact site and difficult to distinguish, but sieve-tube elements of O. cumana and sunflower could be differentiated according to their plastid ultrastructure. While O. cumana sieve-element plastids were larger, often irregular in shape and contained few, small starch inclusions, sieve-element plastids of the host were significantly smaller, always roundish with more and larger starch inclusions. This made it possible to trace the exact contact site of host and parasite sieve elements to show a direct symplastic phloem connection between the two species. The interspecific sieve plate showed more callose on the host side. This allowed detection of newly formed plasmodesmata between host sieve-tube elements and parenchymatic parasite cells, thus showing that undifferentiated cells of the parasite could connect to fully differentiated sieve elements of sunflower. Furthermore, the arrangement of phloem within the O. cumana tubercle as well as differences in sieve-element plastid ultrastructure during shoot development in O. cumana were investigated and are discussed in this paper.

Metabolic Investigation of Phelipanche aegyptiaca Reveals Significant Changes during Developmental Stages and in Its Different Organs

Phelipanche aegyptiaca Pers. is a root holoparasitic plant considered to be among the most destructive agricultural weeds worldwide. In order to gain more knowledge about the metabolic profile of the parasite during its developmental stages, we carried out primary metabolic and lipid profiling using GC-MS analysis. In addition, the levels of amino acids that incorporate into proteins, total protein in the albumin fraction, nitrogen, reduced sugars, and phenols were determined. For the assays, the whole plants from the four developmental stages-tubercle, pre-emergent shoot, post-emergent shoot, and mature flowering plants-were taken. Thirty-five metabolites out of 66 differed significantly between the various developmental stages. The results have shown that the first three developmental stages were distinguished in their profiles, but the latter two did not differ from the mature stage. Yet, 46% of the metabolites detected did not change significantly during the developmental stages. This is unlike other studies of non-parasitic plants showing that their metabolic levels tend to alter significantly during development. This implies that the parasite can control the levels of these metabolites. We further studied the metabolic nature of five organs (adventitious roots, lower and upper shoot, floral buds, and flowers) in mature plants. Similar to non-parasitic plants, the parasite exhibited significant differences between the vegetative and reproductive organs. Compared to other organs, floral buds had higher levels of free amino acids and total nitrogen, whereas flowers accumulated higher levels of simple sugars such as sucrose, and the putative precursors for nectar synthesis, color, and volatiles. This suggests that the reproductive organs have the ability to accumulate metabolites that are required for the production of seeds and as a source of energy for the reproductive processes. The data contribute to our knowledge about the metabolic behavior of parasites that rely on their host for its basic nutrients.

Primary metabolic profiling of Egyptian broomrape (Phelipanche aegyptiaca) compared to its host tomato roots

Broomrape (Phelipanche aegyptiaca) is a root holoparasitic plant considered among the most destructive agricultural weeds worldwide. In order to acquire more knowledge about the metabolism of broomrape and its interaction with its tomato host, we performed primary metabolic profiling using GCMS analysis for the early developmental stage of the parasite and of infected and non-infected roots. The analysis revealed that out of 59 metabolites detected, the levels of 37 significantly increased in the parasite while the levels of 10 significantly decreased compared to the infected roots. In addition, the analysis showed that the levels of total protein in the albumin fraction, reducing sugars (representing starch) and total phenols increased by 9.8-, 4.6- and 3.3-fold, respectively, in the parasite compared to the roots. These changes suggest that P. aegyptiaca has its own metabolism that differs significantly in its regulation from those found in their host. In addition, the results have shown that the levels of most of the metabolites in the infected roots were similar to levels detected in the non-infected roots, except for seven metabolites whose levels increased in the infected versus the non-infected roots. This suggests that the parasite did not significantly affect the host primary metabolic pathways.