We explored the seed-associated bacterial endophytic microbiome in seeds of the endemic holoparasitic species Cistanche armena from a saline and arid habitat in Armenia. A combination of culture-dependent and molecular techniques was employed for identifying the seed endomicrobiome (culturable and unculturable). From surface-sterilized seeds, 10 phyla, comprising 256 endophytic bacterial genera, were identified. Of the culturable strains, we also investigated the plant growth-promoting (PGP) traits. Most of the isolates were spore forming, halotolerant and alkaliphile Bacillus spp., indicating that the endophytic bacteria of C. armena seeds own traits related to the natural habitat of their host plant. Our results confirm that Bacillus species are common and dominated endophytes from plants growing on saline and arid soils. Pantoea spp. and Stenotrophomonas spp. are more favourable PGP endophytes in seeds of C. armena. The PGP traits of these bacteria, such as production of indole, a precursor of auxin, ACC-deaminase and organic acids have the potential to improve the tolerance of their host plants against the abiotic stresses present in their natural habitat. To the best of our knowledge, this is the first report concerning bacterial seed endophytes of the C. armena.

Field dodder is an obligatory stem and leaf plant parasite that causes significant damage in field and vegetable crops in all agricultural regions of the globe. Selective and effective measures to control the parasite are extremely limited. In recent studies, we have shown that granular formulations of dinitroaniline cell division–inhibiting herbicides applied after crop establishment and before dodder germination fit our dodder control strategy and kill the parasite effectively and selectively. The aim of our study conducted from 2014 to 2018 was to evaluate the efficacy and selectivity of granular pendimethalin for dodder control in chickpea under laboratory, greenhouse, and field conditions. Petri dish experiments revealed that the herbicide reduces dodder seed germination while its main effect is a restriction of shoot elongation. Greenhouse experiments demonstrated that the inhibition and distortion of dodder shoot growth impede shoot twining and prevent attachment to the host plant. In dose–response experiments conducted in the greenhouse, we observed that half the recommended rate of granular pendimethalin provides efficient dodder control with no damage to chickpea seedlings. In 3 yr of chickpea field trials, GPM applied across the seeding bed at the recommended rate resulted in high crop yields that were not significantly different from those observed for the untreated no-dodder control, while half of the recommended dose efficiently controlled dodder and other weeds with no damage to the crop, resulting in significantly increased chickpea yields and profitability. These studies indicate that GPM can provide efficient and selective dodder control in chickpea.

Witchweed [Striga asiatica (L.) Kuntze] seeds conditioned for 3 weeks in either water or 0.01% (w/v) sodium hypochlorite (NaOCl) had 83 to 95% germination after being treated with dl-strigol, kinetin, zeatin, or natural stimulants from corn (Zea mays L.) root exudates. None of these compounds, however, induced germination of seeds conditioned in 0.025 or 0.050% (w/v) NaOCl. Seeds conditioned in 0.075, 0.1, or 0.15% (w/v) NaOCl had 8, 56, and 76% germination, respectively, during the first week of conditioning and 10, 100, and 100% germination after 2 weeks of conditioning. Germination in these concentrations of NaOCl was termed “atypical”.

Leaching of dl-strigol at six rates between 0.3 and 4.5 kg/ha through columns of sandy loam soil was estimated using a witchweed [Striga asiatica (L.) Kuntze # STRLU] germination bioassay. After 21 days of leaching daily with 1.27 cm of simulated rainfall, about 86% of the applied chemical remained in the top 2.5 cm of the soil, about 6% in the zone between 2.5 and 7.5 cm, and less than 1% in the soil at depths between 7.5 and 30 cm. However, even with the lowest rate of the chemical application, sufficient dl-strigol was leached to a soil depth between 22.5 and 30 cm to cause most, if not all, of the witchweed seeds to germinate. These results suggest that dl-strigol has a potential for use as an effective tool for a witchweed control or eradication program. No significant degradation of the chemical occurred in moist soil during the 21-day period.

The conditioning and germination processes of witchweed [Striga asiatica (L.) Kuntze] seeds were regulated by synthetic dl-strigol (ST) or natural stimulants (STM) present in a corn (Zea mays L.) root-exudate solution. Seeds conditioned in water for 7 and 14 days required 10−10 and 10−12M ST, respectively, to induce maximum germination (ca. 80%). Surprisingly, conditioning seeds in ST or STM had an adverse effect on the responsiveness of the seeds to the same compounds after conditioning. Compared to seeds conditioned in water, these ST- or STM-conditioned seeds required not only higher concentrations of ST or STM to induce maximum germination, but also longer immersion time to become conditioned. ST or STM inhibits conditioning and thus the regulation of germination by ST or STM depends mainly on the stage of conditioning of seeds when they are exposed to ST or STM. ST or STM stimulates germination only after a pre-germination threshold is reached during conditioning. Exposure of seeds to ST or STM before this critical level is reached apparently inhibits conditioning.

Thirty compounds that are precursors, analogs, derivatives, or fragments of strigol were prepared and tested for their activity as witchweed [Striga asiatica (L.) Kuntze] seed-germination stimulators. Five compounds showed significant stimulatory activity. Among these were 5-ethoxy-3-methyl-2(5H)-furanone, 3-hydroxy-2,6,6-trimethylcyclohex-1-ene-1-carboxaldehyde, a two-ring analog of strigol, and two isomers of a three-ring analog. Several of the other 25 compounds showed slight and/or non-reproducible activity when dimethylsulfoxide was used as the carrier at 0.1% (v/v) in aqueous solutions. Compounds with such diverse structures as trimethylcyclohexenes, furanones, and bicycloheptenones were among those that possessed some stimulatory activity.

Field dodder is a parasitic plant that attaches to the stems and leaves of broadleaf plants, including weeds, field crops, vegetables, and ornamentals, throughout most agricultural regions of the world. Effective field dodder control is extremely difficult to achieve, due to the nature of attachment and close association between host and parasite, which requires a highly effective and selective herbicide to destroy the parasite without crop damage. Previous studies have demonstrated the tolerance of certain tomato varieties to dodder parasitism. The aim of the present study was to evaluate the ability of sulfonylurea herbicides to control field dodder under greenhouse and field conditions. Two greenhouse studies and three field studies were conducted to evaluate the efficiency and crop selectivity of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, halosulfuron, and flazasulfuron in controlling field dodder parasitizing tomato plants. Sulfosulfuron at 50 or 100 g ai ha−1 was effective and safe for tomato in field dodder control, while the other herbicides exhibited little or no dodder control.

Parasitic plants, including the root holoparasites Orobanche spp., cause devastating damage to crops worldwide. Arabidopsis thaliana is widely used as an amenable model plant system to study host–pathogen interactions. Understanding the molecular basis involved in host–parasite interactions will provide practical tools for the detection of genes responsible for incompatibility and resistance responses. In preliminary petri dish experiments, A. thaliana induced seed germination of O. aegyptiaca, O. minor, and O. ramosa at the rate of 87, 72, and 67% of maximum seed germination, respectively. Arabidopsis thaliana induction of O. crenata and O. cumana seeds was negligible (less than 2% of maximum germination). In additional polyethylene bag studies, A. thaliana was parasitized by O. aegyptiaca, O. ramosa, and O. minor resulting in 12, 5, and 2 parasites per host plant, respectively. The results facilitate the use of A. thaliana in host-parasitic plant interaction research.

The members of the genus Cuscuta (common name: dodder) are obligate holoparasitic plants that are found throughout the agricultural regions of the world. Of all of the species of dodder, field dodder (Cuscuta campestris) causes the most damage to crops. This species parasitizes the shoots of broadleaf plant crops and weeds. We conducted a series of field dodder seed germination tests in controlled-temperature chambers, in order to describe the effect of temperature on field dodder germination and develop a germination model based on the obtained data. The best fit was obtained when temperature data and time were transformed to thermal time using the beta-function model. The field dodder germination model can serve as a tool for knowledge-based predictions of germination and emergence timing, to allow for the implementation of effective mechanical and chemical management measures.

Dodder (Cuscuta) species are obligate shoot parasites that attach to stems and leaves of plants belonging to diverse families, diverting water, minerals, and metabolites, resulting in suppression of crop plants and yield reduction. Lespedeza dodder has the most diverse and numerous host range among the Cuscuta genus and is a major weed problem in tomato production in certain parts of the world, including California. At present, few resistant varieties of normally susceptible plant species have been developed or identified, and none are available in California. In this study, greenhouse and field studies were conducted to test and characterize the tolerance of commercial hybrid tomato varieties to lespedeza dodder. In greenhouse studies, Heinz varieties ‘9492’, ‘9553’, and ‘9992’ exhibited tolerance to the parasite, compared to the susceptible variety, ‘Halley 3155’. Lespedeza dodder germinated, made contact, twined around tomato stems, and adhered to them, but in most cases, haustoria failed to penetrate into the stem, eventually leading to the death of the parasite. In field studies, lespedeza dodder attachments were 75% less on tolerant varieties, and dodder growth was reduced by more than 70%.

Crenate broomrape is a major constraint for legume production in Mediterranean and East Asian countries. Resistance to this parasitic weed is scarce in many legumes but is common in chickpea germ plasm. A detailed in vitro study has shown that resistance in chickpea is the result of the combination of at least two mechanisms. First, and most importantly, the two chickpea lines studied have been identified with low rates of stimulant production. Once germination is induced by exogenous applications of the synthetic germination stimulant GR24, thus overcoming the primary resistance mechanism in these lines, a second resistance mechanism is apparent. This is evidenced by a darkening of host cell tissue in contact with the broomrape radicle, leading to failure of establishment, which was frequently observed in the chickpea accessions. Anatomical studies have shown that this apparently “hypersensitive” response does not correspond with the death of host cells in contact with the parasite cells but corresponds to blocking and death of the penetration structures of the parasite.

Flooding is an inexpensive cultural practice used for pest management in Massachusetts cranberry (Vaccinium macrocarpon Ait.) production. This project examined the use of short-term floods (<72 h) for dodder (Cuscuta gronovii Willd.) management under controlled conditions. Using incubators, seed was submerged in water for 0, 24 and 48 h at 10, 15 and 20°C (simulating spring water temperatures) and 0, 12, 24, 36 and 48 h at 15, 20 and 25°C (simulating summer water temperatures). Two 1-year controlled studies (field and greenhouse) evaluated three flood durations (0, 24 and 48 h) and four flood initiations (1, 2, 3 and 4 weeks after early seedling emergence (AEE)). Treated seeds were planted to cranberry vines and to Petri dishes; percent germination, degree of dodder attachment and dodder biomass data were collected. Treatments had limited effect on seed germination. Flooding 4 weeks AEE resulted in the lowest mean attachment ratings and dodder stem biomass on cranberry. This preliminary work provides evidence that flooding may retard dodder stem growth rather than reducing seed germination and that floods initiated after some time has elapsed after early emergence may be more effective than those initiated closer to the time of seedling emergence. More information is needed to thoroughly understand the processes involved; however, small projects such as this can provide interim guidelines that growers can immediately consider when deciding on a dodder management program.

Strigolactones are apocarotenoids regulating shoot branching. They are also known to be exuded by plant roots at very low concentrations, stimulating hyphal branching of arbuscular mycorrhizal fungi and germination of root parasitic weed seeds. We show that strigolactones play a major role in host specificity of Orobanche and Phelipanche (the broomrapes) seed germination. This observation confirms that host-derived germination stimulants are an important component determining the host specificity of these parasitic plants. Weedy broomrape species were less specialized in germination requirements than the non-weedy species except for O. cumana and O. foetida var. broteri. Similar results were obtained with the root exudates. Some species, such as P. aegyptiaca and O. minor, showed a broad spectrum of host specificity in terms of seed germination, which was stimulated by exudates from the majority of species tested, whereas others, such as O. cumana, O. hederae and O. densiflora, were highly specific. Some species, such as O. minor, P. aegyptiaca and P. nana, were responsive to the three strigolactones studied, whereas others were induced by only one of them, or did not respond to them at all. The synthetic strigolactone analogue GR24, generally used as a standard for germination tests, was not effective on some Orobanche and Phelipanche species. Seeds of some species that did not respond to GR24 were induced to germinate in the presence of fabacyl acetate or strigol, confirming the role of strigolactones in host specificity.

The implementation of new uses for traditional cultural and pest management practices has been prompted by renewed interest in sustainable approaches for farming. The use of floods (for various durations) has been an inexpensive and historical cultural practice in cranberry (Vaccinium macrocarpon Ait.) horticulture. The onset of a serious economic crisis in the cranberry industry in 1999–2000 brought about an urgent need to find inexpensive methods of pest control that would allow growers to remain fiscally solvent. Initially, anecdotal evidence from several farms indicated that holding short-term spring floods suppressed dodder infestations. Based on these findings, a 2-year demonstration-style project was initiated in 2002 to determine the efficacy of short-term floods (24–48 h) for the management of dodder in cranberry in Massachusetts. The project was expanded to include evaluating a 10-day summer flood for control of broad-leaved weed species at one commercial cranberry farm. Species richness and diversity and percentage weed coverage were lower after the implementation of the 10-day flood period compared to pre-flood assessments. Weed species dead or not detected after the 10-day flood included ground nut, asters, narrow-leaved goldenrod, chokeberry and poison ivy. Comparison of paired sites (flooded and nonflooded bogs) indicated dodder stem dry weights were lower on flooded areas in three out of the seven locations in year 1. At two additional locations, the flooded bog had higher stem weights when paired with a historically low-infestation bog, which may have masked any dodder reduction from the flooding practice. In year 2, no differences in the number of germinated seedlings between any treatment pairs were noted. Data from a cranberry company representing 12% of the cranberry acreage in Massachusetts indicated a 65–89% reduction in pesticide use when short-term spring floods were implemented during 2001–2003 compared to the previous 3-year period. Short-term flooding may offer a sustainable option that can be integrated into the overall management plan for several problematic cranberry weed species, especially dodder. Additional research is warranted to further define the most effective environmental conditions needed and to validate the efficacy of short flooding events for effective cranberry weed management.