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The southern U.S. produces over 1 billion pine seedlings for market sales per year, with prices varying from 50 to 435 dollars per thousand seedlings. An accurate inventory of seedlings provides nursery management with insights into how many seedlings can be sold and/or if there is any loss due to washout, mechanical damage, or pest/diseases that can still be mitigated. In this study, we developed a system to count pine seedlings at production sites and map the seedling density in the field. A system with three cameras was developed to collect video from different drills in the seedling bed. The videos were preprocessed to restrict the region of interest to the center portion of the image in each camera and separated each drill into individual videos. Two different modalities, i.e., video and optical flow, were evaluated as inputs to a convolutional neural network followed by a long short-term recurrent network to model the sequence of frames and regress to the seedling count for each plot. The mean absolute percentage error (MAPE) of our best performing model was 7.5%, which is an improvement over the baseline manual sampling-based approach with a MAPE of 11%. The results showed that the proposed approach was able to count seedlings in a crowded scene under complex field conditions with higher accuracy than the standard manual practice. Therefore, the proposed system and results demonstrated the potential to replace manual counting and even provide further information such as a seedling density map over the field for precision forest nursery management and seedling harvesting. [ABSTRACT FROM AUTHOR]

The course of the bark beetle-vectored fungus, Leptographium terebrantis S. J. Barras and T. J. Perry, in stemwood growth loss of declining pines in the southeastern United States was assessed in a 13-year-old loblolly pine (Pinus taeda L.) plantation near Eufaula, Alabama, U.S.A. Using stem inoculation as a surrogate for root infection, we hypothesized that L. terebrantis infection impairs sapwood function and thus limits the tree leaf area (AL), new root production, and stemwood growth. Sterile toothpicks colonized by L. terebrantis at varying inoculum densities was used to elicit host growth responses. In the third year after inoculation, the root pathogen reduced the foliage moisture content, whole-tree leaf area (AL), the ratio of AL to tree sapwood area (AS), and stemwood growth in trees receiving the high inoculation treatment relative to those receiving the low or medium inoculation treatments, or the wound or control treatments after seven months of water deficit. The absence of a similar response to water deficit among trees that were noninoculated, wounded, or inoculated at the low or medium densities suggests that, in the loblolly pine–L. terebrantis pathosystem at our study site, the physiological stress caused by water deficit and the high inoculum density was required for the pathogen to elicit a stemwood growth loss. Thus, in loblolly pine forests of the southeastern United States, where climate and soil conditions yield prolonged periods of physiological stress, the presence of L. terebrantis has the potential to reduce stand volume and widen the gap between the predicted and actual stemwood production. [ABSTRACT FROM AUTHOR]

Cogongrass (Imperata cylindrica), an invasive grass species native to Asia, has been shown to reduce tree vigor in loblolly pine (Pinus taeda) plantations, which comprise more than 50% of growing stock in commercial forests of the United States. I. cylindrica produces exudates with possible allelopathic effects that may influence abundance of P. taeda symbionts, such as soil microbes and ectomycorrhizal fungi. Soil microbial communities and root colonization by mycorrhizal fungi were sampled in intensively managed P. taeda stands in Greene County, Mississippi, in I. cylindrica present and absent plots. I. cylindrica present plots had reduced abundance of ectomycorrhizal colonization of pine fine feeder roots in the top 40 cm of soil in comparison to I. cylindrica absent plots. Abundance of pine fine feeder roots in the 21-40 cm and 41-60 cm layers of the soil profile was also reduced in I. cylindrica present plots. Vegetative diversity was negatively correlated with I. cylindrica (% cover), which probably contributed to the reduced microbial diversity in I. cylindrica present plots. Because of the variety of roles microorganisms play, changes associated with the invasion of I. cylindrica are likely to alter nutrient cycling and reduce site productivity. [ABSTRACT FROM AUTHOR]

Root diseases are expected to become a greater threat to trees in the future due to accidental pathogen introductions and predicted climate changes, thus there is a need for accurate and efficient pathogenicity tests. For many root pathogens, these tests have been conducted in stems instead of roots. It, however, remains unclear whether stem and root inoculations are comparable for most fungal species. In this study we compared the growth and damage caused by five root pathogens ( Grosmannia huntii, Grosmannia alacris, Leptographium procerum, Leptographium terebrantis, and Heterobasidion irregulare ) in root and stem tissue of two Pinus species by inoculating mature trees and tissue amended agar in the laboratory. Most fungal species tested caused greater damage in roots of both pine hosts following inoculation. The relationship between root and stem damage was, however, similar when most combinations of pathogens were compared. These results suggest that although stem inoculations are not suitable for determining the actual damage potential of a given species, they may be viewed as a useful surrogate for root inoculations when comparing the relative pathogenicity of multiple species. When grown on amended agar, fungal species generally had greater growth in stem tissue, contrasting with the findings from tree inoculations. [ABSTRACT FROM AUTHOR]

Fusarium circinatumis an important fungal pathogen ofPinusspecies. In South Africa, it is the most significant pathogen ofPinus patulaseedlings in forestry nurseries where it presents a substantial constraint to productivity and can continue to cause mortality in-field for up to two years after establishment. This study describes the results from two trials whereP. patulaseedlings were inoculated withF. circinatumto determine the impact of the pathogen on nursery and field performance. Seedlings were also subjected to water stress treatments to ascertain whether this would trigger the onset of disease symptoms. Inoculum load and timing of inoculation had significant effects on seedling survival in both the nursery and field. High inoculum concentrations caused greater levels of mortality and, where seedlings were inoculated at a young age, they showed higher levels of susceptibility toF. circinatum. Temporary water-stress in the nursery produced smaller plants and improved in-field survival, but this treatment did not trigger higher mortality in inoculated treatments. On the other hand, transplant stress was a major contributor to the higher levels of mortality observed in inoculated treatments. Overall, these studies confirmed that infection in the nursery leads to the disease problems observed during early plant establishment in the field. [ABSTRACT FROM AUTHOR]

Leptographium terebrantis has been implicated as a contributing factor of P. taeda decline and mortality over the past several decades. We examined the potential of L. terebrantis to cause decline symptoms and determined the relationship between pathogen spread and the formation of new sapwood. The study was undertaken in a 13-y-old P. taeda plantation using artificial inoculations of fungal-colonized, sterilized toothpicks. We found that L. terebrantis was not only re-isolated from dying inoculated trees but caused decline symptomology and mortality at a high inoculum density. It was found that 20% mortality and severe growth loss among surviving trees occurred with L. terebrantis infection at the high density. At lower inoculum densities, trees produced a complete ring of new sapwood that appeared to sustain tree physiology. This suggests that management practices in P. taeda plantations which minimize bark beetle infestation and pathogen inoculum densities allow adequate sapwood function for sustained growth. • Leptographium terebrantis causes P. taeda tree mortality at high inoculum density. • Some P. taeda trees, however, tolerate the fungus at high inoculum density. • At lower inoculum densities, P. taeda completely tolerates L. terebrantis infection. • Tolerant trees form a continuous or partial sapwood without the fungal infection. [ABSTRACT FROM AUTHOR]

Bark beetle‐vectored ophiostomatoid fungi, Leptographium terebrantis, is inoculated on the roots and lower stems of stressed Pinus species during the feeding activity of bark beetle. To determine the exact host response following inoculation, it is critical to challenge the host with a realistic amount of fungal inoculum. Thus, we designed a series of stepwise experiments using L. terebrantis colonized toothpicks which focused on the inoculum transfer from the toothpicks to excised Pinus taeda stem segments and living saplings, respectively, at different inoculum densities. The toothpicks served as a substrate for fungal growth and sporulation and the inoculation showed their utility in eliciting host's response to the pathogen. The inoculated fungus caused blue‐stain and sapwood occlusions in P. taeda stems and saplings, respectively. The volume of occluded, visually damaged sapwood increased by 1.96 cm3 per radial inoculation point on average. Fungal colonized toothpicks can be used as a suitable alternative to agar discs for studying bark beetles vectored fungi and their host interactions. [ABSTRACT FROM AUTHOR]