Although shape shows a negative relationship with biomass, this influence is minimal when compared with photosynthesis . However, leaf shape shows the largest influence on both yield and fruit BRIX, with photosynthesis second, and is the only positive contributor to yield . This positive correlation is from rounder, Potato Leaf Morph-like leaves, while narrower leaves have the opposite effect based on the PC contributions to leaf shape. The negative effect of photosynthesis on tomato fruit yield and the strong contribution of leaf shape to yield and BRIX are novel findings that run counter to the interpretation of fruit quality improvement, as increased photo assimilate should result in more available sucrose to stronger sinks such as fruit . To test the model performance we used PLSPREDICT on the entire heirloom dataset used to build the structural model. Table S8 shows the mean absolute percentage error and Q2 value for the complete model. We also used part of the dataset that included ABC Potato Leaf and Aunt Ginny’s Purple in a similar analysis . The complete model has c. 20–30% error for each LV, which is expected given the diversity of genotypes in the dataset, with fruit weight giving the highest MAPE, at 93.2% . The Q2 value for most variables is positive and shows that they have relevance in the predictive performance, with the exception of leaf sugar, which is slightly negative . In the case of ABC Potato Leaf and Aunt Ginny’s Purple, two lines selected randomly to test the model on individual cultivars, round plant pot a significant increase in Q2 and decrease in MAPE is seen for all LVs except leaf sugar . This indicates that the model is substantially stronger in predictive performance for individual cultivars, but also predicts well with the complete model.
To evaluate the predictive performance of our model on additional datasets, we used data from two other cultivars grown in the same field, M82 and Lukullus, that were not used to construct the model. PLSPREDICT was used in SMARTPLS 3.0, along with the structural model constructed using the heirloom cultivars, to test the model performance by use of training sets and hold out samples, both taken from the M82/Lukullus dataset. By using the leaf shape PC values, we were able to compare the predicted mean values for the remaining MVs, or the predicted measured values, against the actual measured values and evaluate the relative performance of the model. Tables 2 and 3 show the results for M82 and Lukullus, respectively. PC values for leaf shape are not included as they are input variables and used for predicting the other values. For M82 the predicted median values compared with the actual median values showed under 1% difference for all except leaf complexity, which had a percentage difference of 8.42% . This indicates that the model was underpredicting the leaf complexity of M82 by c. 8%. Lukullus-predicted values were also under 1% different, except for leaf complexity and stomatal conductance which varied by 2.56% and 1.31%, respectively . In addition to the predicted values PLSPREDICT also tests the model performance and reports the root mean square error, mean absolute error, and MAPE for each of the MVs tested . The MAPE shows the accuracy of the predictions, with lower percentages representing better performance. Leaf complexity for both cultivars showed the largest MAPE values, 201.2% and 26.5% in M82 and Lukullus, respectively .
The M82 MAPE indicates that the model does not predict leaf complexity well for mid-level complexities such as 18 but does improve at high-end leaf complexities near 40 . Most heirloom cultivars had low leaf complexities , potentially explaining the poor performance in predicting leaf complexity for M82. Contrary to previous findings , we found that leaf complexity does not impact yield or BRIX, and only impacts vegetative biomass, so this inaccuracy would only impact vegetative output predictions by the model. Lukullus has indeterminate growth like the heirlooms analyzed here, but M82 is determinate; however, the predictive accuracy of the model was still good, indicating its usefulness in assessing field performance of other tomato cultivars.The primary focus of crop improvement has been on fruit traits and photosynthesis , with some studies focusing on how sugars are moved from source to sink. Despite heirloom varieties with the Potato Leaf Morph being prized for fruit quality by the gardening community, vegetative traits such as leaf shape have been relatively ignored in breeding efforts. In this study we investigated the role of leaf shape on fruit quality by measuring both input traits and output traits for 18 heirloom cultivars. All these cultivars were classified as Potato Leaf, but varied greatly in their leaf shapes, development, and fruit quality . We found that these lines do not vary significantly in overall photosynthetic capacity, or their usage of light when available , suggesting that the variation in BY among these cultivars was not a result of improved/decreased photosynthetic capacity. While our measurements for photosynthesis do not show significant difference when PAR is available, the PARi differed between cultivars based on their growth patterns . All cultivars exceeded 1200 lmols m 2 s 1 of PARi but varied in the later weeks between 1200 and 2000 lmols m 2 s 1 . Combining multiple complex physiological and morphological measurements into informative relationships has proven difficult and has limited our understanding of how these different traits impact each other .
Focusing on any one part, such as photosynthesis or fruit sink strength, while providing improvements , occurs at the expense of a comprehensive understanding of the overall relationships between these traits. Analyzing the individual PCs revealed significant differences in leaf shape among the heirloom cultivars, with several having stronger Potato Leaf Morphs and higher BY values , with some correlation between these traits. Potential epidermal shape changes that could arise from leaf shape changes and that could influence yield would relate to stomatal number. A previous study in 2002 analyzed several tomato cultivars developmentally and histologically and found no real differences between these cultivars. This and another study in 2010 suggest that there are no gross anatomical differences between these tomato cultivars. We used PLS-PM to combine all these measured traits, using the modeled final harvest data as input to find causative relationships . Strong relationships among gas exchange, light, and photosynthesis were expected, along with a strong positive effect of photosynthesis on vegetative biomass . Photosynthesis has a strong positive effect on fruit BRIX, both directly and indirectly . Increased photosynthesis results in lowered leaf sugar content, and a concomitant increase in fruit BRIX. It is possible that increased sugar production from photosynthesis results in higher rates of transport of sugars out of the leaves and into sinks. The mechanisms that regulate source–sink relations and sugar distribution are still not fully understood on a whole-plant physiological level ; however, based on our model, increased photosynthesis negatively impacts total yield . While photosynthesis does lead to increased sugar production and is shown in our model to drive higher sugar content within existing fruit, it does not provide a means to increase yield. Leaf shape, specifically rounder, less lobed leaves, round garden pot has a positive effect on both fruit BRIX and yield . Of all the factors measured here, only leaf shape positively influenced yield, with other paths having negative influences . Rounder leaves still drive slightly increased photosynthesis indicated by the thin arrow , which results in increased fruit BRIX. This path should also result in decreased yield. However, leaf shape has a strong positive and direct correlation with yield that overcomes the negative impact of photosynthesis and leads to increased yield as well as BRIX . Conversely, with narrow leaflets there is a small negative impact on photosynthesis which should result in increased yield, but narrow leaves have a direct negative impact on yield which is stronger than the photosynthetic pathway . The strong causative relationship among leaf shape, fruit BRIX, and yield suggests that leaf shape impacts both highfruit BRIX and increased number of fruits, probably by modulating sugar distribution, therefore bypassing the direct impacts of photosynthesis itself . How leaf shape affects this distribution is unclear, as it does not act directly through leaf sugar content, or through strong regulation of photosynthesis to improve yield . A recent study looked at the diversity of leaf shape in sweet potato . Any correlations between leaf shape and yield traits in this species would be of interest and help to establish general principles. The whole-genome phylogenetic analysis of 23 tomato cultivars showed many of the Potato Leaf Morph cultivars were closely related to each other, with the exception of Brandywine, though it did not show the origin of the C-locus mutation .
To address this and identify if this morphology was selected for in breeding, we performed PHYLONETWORKS analysis . This analysis showed several hybridizations between Potato Leaf Morph and nonPotato Leaf Morph cultivars, and probably a unique incidence of the C-locus mutation in Prudens Purple . PHYLONETWORKS analysis of chromosome 1, 6, and 12 specific common SNPs each showed unique hybridization events, distinct from those seen in the WGS analysis . The PHYLONETWORKS analysis suggests multiple hybridization events with Potato Leaf Morph-containing cultivars. Potato leaf cultivars have been suggested to increase disease resistance compared with regular leaf varieties and may have been selected for this reason or for other as yet-unknown benefits present. We have shown that leaf shape strongly impacts the overall fruit quality in tomato, with rounder, less lobed leaves giving rise to higher yield and higher fruit BRIX. Photosynthesis, surprisingly, has a negative impact on yield while still positively contributing to fruit BRIX. Using data from cultivars not included in making our path model, we also showed that the model has a strong predictive performance for linking leaf shape to BY and could be used to potentially predict the outputs of a cultivar using leaf shape data . Our work shows the importance of leaf shape to yield and BRIX across a wide array of genetic backgrounds, implicating leaf morphology in playing a significant and previously unidentified role in tomato fruit quality.The absence of leaves in winter provides a clear view of the framework of the tree and the opportunity to thin or head any branches. The amount of dormant pruning will be less if trees receive appropriate summer training and pruning. For pest and disease control, prune out any dead, diseased, crossed, or broken branches as well as water sprouts and root suckers. Remove and destroy all diseased wood. Periodically disinfect cutting tools with a sanitizing liquid or a 1:1 bleach and water solution during pruning and at any time tools come into direct contact with diseased tissue. Oil shears immediately after use to avoid corrosion. Paint the trunk and lower branches of young trees that are exposed to hot afternoon sun with a 1:1 mixture of white interior latex paint and water to prevent sunburn injury and reduce borer infestations. Apply the paint mixture from 2 inches below the soil line to 2 feet above.Sanitation is necessary to prevent disease and pests and reduce the need for sprays. If possible, rake and dispose of all leaves after they drop and before the first rains. Remove and destroy over-wintering fruit in the tree and on the ground to eliminate sources of insects and diseases the next season.Oils used at this time of year include insecticidal oils, narrow range, supreme, or superiortype oils. A supreme or superior-type oil spray, applied during the delayed dormant period just as eggs are about to hatch, should keep European red and brown mites below damaging levels if predators are not disrupted by sprays for other pests. Supremeor superior-type oils will kill overwintering eggs of aphids on fruit trees if applied as a delayed dormant application just as eggs are beginning to hatch in early spring. These treatments will not give complete control of aphids and are probably not justified for aphid control alone. Dormant oil sprays alone DO NOT control oriental fruit moth, navel orange worm, peach twig borer, or two-spotted and Pacific spider mites. Dormant disease control applications use materials such as copper, lime sulfur , Bordeaux , or a synthetic fungicide to limit infection and prevent the spread of certain fungal diseases like leaf curl, shot hole, powdery mildew, and scab.A dormant spray may not be warranted every year in the backyard orchard except where peach leaf curl is consistently a problem.