Eggplant, or brinjal, is one of the most consumed and important tropical solanaceous vegetable crops grown worldwide. Little leaf is a disease associated with the presence of phytoplasmas especially widespread in brinjal in India. To clarify the epidemiology of this disease, a verification of its transmission through seeds to seedlings and their progeny derived from symptomatic mother plants was performed. Brinjal seeds field-collected in the Dharwad district of Karnataka State, India, were sowed in a greenhouse under insect-proof conditions. DNA was extracted from seedlings and their progeny and from symptomatic plant samples collected in the field. The first- and second-generation seedlings obtained *under these conditions were tested at various time points after germination by amplification of the 16S rRNA gene of phytoplasmas. The amplicons obtained were subjected to restriction fragment length polymorphism (RFLP) analysis and sequencing for the identification of detected phytoplasmas. Ribosomal groups 16SrI, 16SrII, 16SrIII, 16SrV, 16SrVI, and 16SrXII were identified. Moreover, a number of fruits produced from the first-generation seedlings showed precocious seed germination, and the young seedlings resulted as phytoplasma-positive. The seed transmission of phytoplasmas in eggplants for two subsequent generations highlights the risk of additional sources of infection of the disease represented by asymptomatic and infected seedlings in the presence of insect vectors. The seed transmission could explain the continuous presence of epidemic outbreaks of phytoplasmas in brinjal cultivations in several cultivation areas.

The knowledge of phytoplasma genetic variability is a tool to study their epidemiology and to implement an effective monitoring and management of their associated diseases. ‘Candidatus Phytoplasma solani’ is associated with “bois noir” disease in grapevines, and yellowing and decline symptoms in many plant species, causing serious damages during the epidemic outbreaks. The epidemiology of the diseases associated with this phytoplasma is complex and related to numerous factors, such as interactions of the host plant and insect vectors and spreading through infected plant propagation material. The genetic variability of ‘Ca. P. solani’ strains in different host species and in different geographic areas during the last two decades was studied by RFLP analyses coupled with sequencing on vmp1, stamp, and tuf genes. A total of 119 strains were examined, 25 molecular variants were identified, and the variability of the studied genes was linked to both geographic distribution and year of infection. The crucial question in ‘Ca. P. solani’ epidemiology is to trace back the epidemic cycle of the infections. This study presents some relevant features about differential strain distribution useful for disease monitoring and forecasting, illustrating and comparing the phytoplasma molecular variants identified in various regions, host species, and time periods.

Recent research has demonstrated a presence inside the seeds of several plant species of endophytic bacteria that can directly or indirectly interact with germination and seedling growth. Phytoplasmas are plant-pathogenic bacteria that severely impact the agricultural productivity of several crops, including alfalfa, a crucial forage crop in which seed transmission was reported. Therefore, understanding the transmission pathways of phytoplasmas is essential for developing effective control strategies. This study investigates the seed transmission of phytoplasmas in alfalfa using seeds collected in Oman in 2002 and kept in a dry environment in a laboratory for 20 years. The sterilized seeds were germinated and grown in agar medium under sterile conditions and transplanted in soil under greenhouse-controlled insect-proof conditions. Utilizing polymerase chain reaction (PCR) and nested PCR followed by RFLP and sequencing analyses, the alfalfa seedlings were screened for the phytoplasma presence. The detection of phytoplasmas in 16SrIII, 16SrV, 16SrX, and 16SrXII groups was achieved, confirming the preliminary results obtained in the 2002 testing of the same seed batches. This finding indicates that seed transmission could be a critical pathway for the spread of these pathogens in alfalfa, considering their survival in seeds for more than 20 years. Further investigations into the mechanisms of seed transmission and the development of resistant alfalfa varieties are essential to enhance the sustainability and productivity of alfalfa cultivation, thereby supporting the agricultural sector’s efforts to meet the growing demand for high-quality forages.

Five samples were collected from neem trees exhibiting little leaf and witches’ broom in Gorakhpur, Uttar Pradesh, India during August 2019 surveys. Molecular analyses were conducted for detection, identification and characterization of phytoplasmas associated with this disease. The identity of phytoplasmas detected in neem samples was confirmed through PCR/RFLP analyses using phytoplasma 16Sr RNA gene universal primers and primers amplifying portions of the secA and leu genes. In all the positive samples, the presence of a’ Candidatus Phytoplasma trifolii’-related strain was identified. The phytoplasma identification was confirmed by 100% identity with Ca. P trifolii’ strains. The RFLP analyses on 16S ribosomal gene allowed to determine that this phytoplasma could be enclosed in 16SrVI-D subgroup. RFLP and sequencing analyses on secA gene showed also the presence of a strain related to Ca. P asteris’, indicating the presence of mixed infection with two phytoplasmas. This is the first report of 16SrVI and 16SrI mixed phytoplasma infection in severely symptomatic neem trees.

‘ Candidatus Phytoplasma pyri’, the pathogen associated with pear decline, affects pear trees across both the old and new worlds. However, research on this phytoplasma has been limited by the lack of genomic data. This study presents the first draft genome of ‘ Ca. P. pyri’ using a strain from Chile, with its genomic features analyzed in comparison with the closely related ‘ Ca. Phytoplasma’ species ‘ Ca. P. mali’ and ‘ Ca. P. prunorum’. The draft genome spans 456,478 bp with a GC content of 20.4%. Key genes possibly associated with pathogenicity and potential pathogenic effectors were identified, and they are notably lacking orthologs of known effectors. A single potential mobile unit similar to that of ‘ Ca. P. mali’ was identified. It is characterized by the absence of the transposase tra5 and the presence of the IS3 family transposase iSErh1. Multilocus sequence analysis of six genetic markers (16S rRNA gene, LSU36p, tuf, aceF, secA, and secY) from 10 Chilean and 10 Italian samples revealed high genetic uniformity among the Chilean strains, collected from five geographically distant orchards over a span of 13 months; by contrast, strains with greater diversity were detected among those from Italy, collected from a few localities over approximately 30 years. These findings suggest limited evolutionary divergence of this phytoplasma in Chile. This study provides a foundational framework for investigations into the pathogenic mechanisms and evolutionary dynamics of ‘ Ca. P. pyri’.

Tamarisk witches’ broom, yellowing, and little leaf symptoms were observed during 2018–2023 surveys of rural deserts in central regions of Iran with the highest disease incidence up to 72% in Chah Afzal (Yazd province). A verification of the presence and identity of phytoplasmas associated with these symptoms was then performed. Tamarisk tree branch cuttings obtained from symptomatic plants sprouted up to 90.3% but with 15–25 days’ delay compared to the asymptomatic ones and showed internode shortening and witches’ broom, while the branch cuttings from asymptomatic plants had normal growth and sprouted up to 97.8%. Phytoplasma transmission by dodder bridges to periwinkle did not succeed, while nested polymerase chain reaction on the phytoplasma ribosomal gene followed by RFLP and phylogenetic analyses revealed the presence of ‘Candidatus Phytoplasma asteris’, ‘Ca. P. australasiae=australasiaticum’, and ‘Ca. P. trifolii’ (ribosomal subgroups 16SrI-B, 16SrII-D, and 16SrVI-A, respectively) in the samples from symptomatic plants only. Further amplifications were performed on selected phytoplasma-positive samples on tuf and secA genes, and the produced sequences indicated the presence of mixed phytoplasma infection in some of the samples. In particular, in the tuf gene, a mixed infection of ‘Ca. P. australasiae=australasiaticum’ and ‘Ca. P. trifolii’ was detected, while in the secA gene, the presence of ‘Ca. P. asteris’ or ‘Ca. P. tritici’ strains was identified. The first-time detection of diverse phytoplasma strains in symptomatic T. aphylla suggests that this species represent a relevant source of infection for the agricultural crops and for landscape plants especially when temperature allows insect vector transmission, and therefore, it represents a risk in every environment especially in the frame of climatic changes.