Physical dormancy (PY) in seeds or fruits has been reported in 17 angiosperm families but not in basal angiosperms, magnoliids or gymnosperms. Here, we report PY in fruits (germination unit) of Cassytha filiformis, a parasitic species in the magnoliid clade. Moisture content of fruits ranged from 10% to 16%, and the seeds are orthodox (desiccation tolerant). Manually scarified fruits increased in mass >80% during imbibition, whereas untreated fruits increased <16%, via only a few fruits imbibing. Thus, the fruits are water impermeable. Dye did not penetrate the lignified palisade layer in the endocarp. Dye tracking of innately non-dormant fruits suggested that the carpellary micropyle is the water gap in C. filiformis fruits. Manual scarification broke dormancy of most, but not all, C. filiformis fruits. Thus, a high percentage of the germination units have PY and a low percentage PY + physiological dormancy. This is the first verified report of PY in the magnoliids; PY is now known to occur in four of the five major angiosperm clades. The evolutionary aspects of PY in Cassytha, an isolated genus in Lauraceae, are discussed.

Physical dormancy (PY) in seeds/fruits, which is caused by the water-impermeable palisade layer, has long been considered a mechanism for synchronizing germination to a favourable time for seedling survival and establishment. Recently, a new hypothesis (crypsis hypothesis) was proposed as the main selective factor for the evolution of PY. However, there are some misconceptions in this hypothesis. Our objective is to critically evaluate the crypsis hypothesis and to point out that there are multiple adaptive roles of PY. The fundamental argument in the crypsis hypothesis, that PY evolved as an escape mechanism from predators, is not valid according to the evolutionary theory of Darwin. According to Darwin's hypothesis, variations (dormancy in our case) within a population occur randomly, i.e. there is no direct function of a variation at the time of its origin. Different selection pressures operating in the environment increase or decrease the fitness of individuals with the variation. Water-gap anatomy in seeds/fruits and phylogenetic relationships of species with PY suggest that PY has evolved several times in angiosperms. Thus, we argue that not only predatory pressure but also several other environmental pressures (e.g. proper timing of germination, ultra-drying of seeds, dispersal and pathogens) were involved in increasing the fitness of species producing seeds with PY. The significance of PY in the survival of the species under the above-mentioned environmental pressures and other misconceptions of the crypsis hypothesis are discussed in detail.

Tea (Camellia sinensis [L.] O. Kuntze) is cultivated as a beverage crop. Despite being a hardy perennial, the tea plant is susceptible to various biotic stresses. Among them, the foliar disease blister blight (BB) is considered the most serious threat to the tea industry, particularly in Asia. BB caused by Exobasidium vexans (Basidiomycetes) was first reported from Northern India in 1868 and gradually established in other tea-growing countries. The fungus E. vexans attacks young harvestable shoots and causes 20 to 50% crop loss. Over the past 150 years, scientific research has delved into various aspects of BB disease, including pathogen biology, disease cycle, epidemiology, disease forecasting, crop loss assessment, and disease management strategies. In a recent shift in research focus, scientists have begun to investigate the resistance mechanisms of tea plants against BB and apply this knowledge to commercial tea cultivation. Although progress has been significant in understanding the fundamental aspects of BB resistance, the detailed molecular mechanisms driving this resistance remain under investigation. This paper focuses on the current understanding of defense mechanisms employed by tea plants against E. vexans and, conversely, how E. vexans overcomes these defenses. Furthermore, we discuss the application of plant resistance strategies in commercial tea cultivation. Lastly, we identify existing research gaps and propose future research directions in the field.

Rhizoctonia solani is a basidiomycete phytopathogenic fungus that causes rapid necrosis in a wide range of crop species, leading to substantial agricultural losses worldwide. The species complex is divided into 13 anastomosis groups (AGs) based on hyphal fusion compatibility and further subdivided by culture morphology. While R. solani classifications were shown to be independent of host specificity, it remains unclear whether different R. solani isolates share similar virulence mechanisms. Here, we investigated the infectivity of Japanese R. solani isolates on Brachypodium distachyon and barley. Two isolates, AG-1 IA (from rice) and AG-4 HG-I+II (from cauliflower), infected leaves of both plants, but only AG-4 HG-I+II infected roots. B. distachyon accessions Bd3-1 and Gaz-4 and barley cultivar ‘Morex’ exhibited enhanced resistance to both isolates compared to B. distachyon Bd21 and barley cultivars ‘Haruna Nijo’ and ‘Golden Promise’. During AG-1 IA infection, but not AG-4 HG-I+II infection, resistant Bd3-1 and Morex induced genes for salicylic acid (SA) and N-hydroxypipecolic acid (NHP) biosynthesis. Pretreatment with SA or NHP conferred resistance to AG-1 IA, but not AG-4 HG-I+II, in susceptible B. distachyon Bd21 and barley Haruna Nijo. On the leaves of susceptible Bd21 and Haruna Nijo, AG-1 IA developed extensive mycelial networks with numerous infection cushions, which are specialized infection structures well-characterized in rice sheath blight. In contrast, AG-4 HG-I+II formed dispersed mycelial masses associated with underlying necrosis. We propose that the R. solani species complex encompasses at least two distinct infection strategies: AG-1 IA exhibits a hemibiotrophic lifestyle, while AG-4 HG-I+II follows a predominantly necrotrophic strategy.

Derived from the Camellia sinensis (L.) Kuntze plant, tea is the most widely consumed natural beverage in the world. Tea is a perennial woody plant. Monoculturing tea on a large scale makes it susceptible to many perennial and seasonal diseases. The leaves, stems, and roots of tea plants are susceptible to fungal, bacterial, and viral pathogens. Tea is predominantly grown in Asian and African regions; hence, conventional methods including symptomology and signs, and microbiological and microscopic methods are mainly used in disease diagnosis and pathogen identification. Accurate and rapid identification of diseases and pathogens is imperative for the sustainability of tea plantations. Thus, the technological advancement in plant disease diagnosis also embraces the global tea industry. This chapter discusses new technological advances in tea disease diagnosis, focusing on molecular biological methods, whole genome sequencing, and remote sensing and image analysis methods. Further, it highlights the challenges in disease diagnosis as a perennial woody plant and pins down available opportunities that could be successfully adopted to overcome the issues.