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Litchi is an item of impulse buying, and consumers prefer litchi fruit that is bright red and appealing to the eye. Litchi is exacting in its climatic requirements, and optimal colour development remains a challenge, especially in climes that are far from ideal and shaded portions of the tree canopy. In this study, we tested different bagging combinations involving butter/parchment paper, non-woven polypropylene, polypropylene, high density polyethylene, and black polythene bags, and recorded their effect on colour development and fruit quality in litchi. Our results show how bagging increases red colouration in the pericarp by upto 30%, reduces pest incidence, and improves the overall quality of fruit in litchi. We conclude that optimal fruit quality can be obtained by bagging litchi bunches with a combination of butter paper and polypropylene or non-woven polypropylene bag. Such bright red-coloured litchi fruit with negligible fruit borer infestation can have better consumer acceptability and also fetch better prices for growers.

An experiment on various litchi genotypes in Bihar conditions was carried out at the ICAR-National Research Centre on Litchi, Muzaffarpur, to evaluate the numerous factors responsible for fruit drop at different phases. The primary focus was on determining the phases at which the largest fruit drop occurs and the factors that contribute to fruit drop. The genotype IC-0615608 had the highest fruit set (71.11%) after one week of pollination, while genotype IC-0615587 had the lowest fruit set (20.45%). The genotype IC-0615585 had the highest final fruit set at harvest (9 weeks), while the genotype IC-0615595 had the lowest (0.81%). Genotypes of litchi linked to several causes showed a significant fruit decline. Improper pollination and fertilization, embryo abortion, seed borer and abscission layer were four factors identified which contributed to fruit drop at various stages. Litchi genotypes have been categorized into three categories (low, medium and high fruit drop) based on severity of fruit drop. Improper pollination and fertilization (up to third week), and embryonic abortion (during fourth week) were the main causes of the initial fruit drop. The seed borer infestation abruptly surged in the fifth week, persisted into the eighth week, and then began to significantly decrease in the ninth week. The eighth week saw the beginning of the abscission layer formation, which was the source of the heavy fresh fruit drop that occurred in ninth weeks. Improper pollination and fertilization followed by embryo abortion and infestation of seed borer were the main causes of fruit drop. Knowing the numerous factors connected with the fruit drop at different phases will assist control it better.

This study aims to evaluate the effects of weather on panicle development, flower morphology and fruit set in litchi cv. Shahi. Meteorological data from 2017 to 2018 were documented and panicles were tagged in order to follow the dates of the onset of several floral phenological stages, such as flower bud initiation, panicle emergence, flower opening, fruit set, pulp development, colour break, and fruit maturity. To ascertain the relationship between crop and weather as well as the relationship between temperature and the quantity of female flowers and the sex ratio, statistical analysis was conducted using the two-year combined weather and crop records. Temperature in 2018 during the first flowering phase was lower (Tmax: 17.1 °C and Tmin: 8.4 °C) than in 2017 (Tmax: 21.49 °C and Tmin: 9.50 °C). Low temperatures encouraged the formation of healthy panicles with a higher proportion of female flowers (7.82%), guaranteeing a respectable final fruit set (4.53%) at harvest. The highest yield (83.45 kg/ha) was recorded in the year 2018 as compared to the year 2017 (64.28 kg/ha). Fruit set peaked first and then started to decline at fruit maturity due to a sudden increase in temperature soon after fruit set, which caused a loss of moisture and eventually fruit drop. Thus, lower temperature during floral bud differentiation endured strong panicle development which carried out more female flower and fruit set resulted in the higher yield.

The presence of a narrow genetic base is the major bottleneck in improvements in litchi to get desired objectives. Studies on the nature and extent of genetic diversity are directly related to yield and quality, which can be used in a breeding programme for genetic improvement. In the present study, 30 litchi genotypes were assessed with respect to variability, heritability and genetic advance based on 39 quantitative traits. Results revealed that phenotypic coefficients were lower than their corresponding genotypic coefficients suggesting an inherent relationship among them. High phenotypic and genotypic coefficients of variation were recorded for flavonoids in seeds (132.39 and 132.38%), flavonoids in the pericarp (116.89 and 116.86%), phenolics in the pericarp (97.84 and 97.83%), anthocyanin in the pericarp (55.73 and 55.54%), female flowers (53.08 and 52.98%), total chlorophyll (51.07 and 50.99%), phenolics in seeds (48.60 and 48.58%), number of fruits per cluster (44.94 and 44.73%), tree volume (38.80 and 38.70%) and panicle length (28.15 and 19.92%). Broad-sense heritability was more than 80% for all the traits except trunk girth, leaflet width, panicle length and titratable acidity. Heritability and genetic advance were found to be maximum for female flowers (%), phenolics and flavonoids content. A high coefficient of variation was observed for female flowers (%), number of fruits per cluster, phenolics and flavonoids. The grouping of genotype based on combined qualitative and quantitative traits presented more accurate results. This will help to select distant diverse genotypes in the hybridization programme in order to get more diverse progenies.

Litchi produces difficult-to-store seeds, which is generally thought to be limited by desiccation sensitivity and cold intolerance. Experiments on effect of storage conditions on germination of Shahi, China and Bedana cultivar were conducted at ICAR- National Research Centre on Litchi in 2018 and 2019. Fruits of each cultivar were harvested at maturity and separated into three sub-lots: freshly extracted seeds which were sown immediately; the second and third lots comprised extracted and non-extracted seeds respectively, which were further divided into four sub-lots and stored at room temperature, 4 °C, 0 °C and − 20 °C. Stored seeds were sown for germination at weekly intervals. Fresh seeds exhibited more than 90% germination. More than 50% seeds were viable after 15 days at room temperature and at 4 °C. Freezing temperature storage, on the contrary, resulted in total loss of viability. Intact litchi seeds after 2 weeks fail to germinate.

Fruit load management is becoming increasingly important as a factor related to inconsistent fruit weight and quality, maturity, physiological disorders, and biennial tendencies. ‘Shahi’ is a very important cultivar of litchi, which occupies major area in India. An experimental trial evaluating the effect of fruit load on fruit weight, fruit quality, sun burn, and fruit cracking of ‘Shahi’ litchi was conducted for three consecutive years (2017, 2018, and 2019) to determine the optimal fruit load. The highest fruit weight (27.86 g) was recorded when fruit load per panicle at harvest was 16. Overall, fruit weight decreased as fruit load increased. Acidity and ascorbic acid increased as fruit load decreased but total soluble solids (TSS) increased as fruit weight increased. Sun burn, fruit cracking, and fruit surface temperature (FST) increased as fruit load decreased but maturity increased as fruit load increased. Anthocyanin content of peel decreased as fruit load increased. Overall, the value of L decreased as fruit load increased. The redness of skin decreased as fruit load increased, and the yellowness of fruit increased as fruit load increased. The highest sun burn and fruit cracking were found on the southern side followed by east, west, and north. Fruit load was highly significant and positively correlated with the thickness of the panicle (0.805) and maturity days (0.951), and negatively correlated with sun burn (−0.886), fruit cracking (−0.976), and FST (−0.951). The thickness of the panicle was positively correlated with maturity days (0.846) and negatively correlated with sun burn (−0.968), fruit cracking (−0.953), and FST (−0.804). Fruit weight was positively correlated with TSS (0.962) and anthocyanin (0.798) and negatively correlated with acidity (−0.940) and ascorbic acid (−0.911). Maturity was negatively correlated with FST (−0.942), fruit cracking (−0.943), and sun burn (−0.901). This study will help to decide the retention of fruit load in order to get quality production in ‘Shahi’ litchi.

An experiment was conducted at the ICAR-National Research Centre on Litchi, Muzaffarpur (Bihar), India, during the periods 2018–2019 and 2019–2020 to assess the effect of spacing and training system on morpho-physiology, yield, and quality of litchi. The maximum plant height was found at the spacing of 8 m × 8 m (4.25 m), but the highest increase in plant height during the study period was recorded in close planting T1(4 m × 3 m with supporting system) (30.47%). The highest increase in plant spread was recorded in T1(13.15%), but the highest increases in canopy area were noted in treatment T2(4 m × 3 m without supporting system) (30.86%). Light interception within the canopy was higher in wider-spaced plants. Light interception was highest under wider spacing in the upper canopy (93.31%). The photosynthetic rate (Pn) and stomatal conductance (gs) value were higher in low-density plants. The rate of transpiration was highest (2.38 mmol H2O/m2/s) at the spacing of 8 m × 8 m, and water use efficiency was found to be highest in high-density plants. A higher internal carbon dioxide concentration was found in less densely planted plants. The maximum mesophyll efficiency value was recorded in close-spaced plants. Total nitrogen, phosphorus, and potassium contents were found to be higher in wider-planted plants. The number of panicles per branch increased in wider spacing. The maximum fruit yield per plant (46.79 kg/plant), fruit weight (22.04 g), and total soluble solids (20.40 0B), as well as maximum total sugar (15.10%) and organoleptic score of fruit (8.45) were recorded under the wider spacing system of planting.

The present study was conducted during 2018 and 2019 at the ICAR-National Research Centre on Litchi Muzaffarpur, Bihar, India, to standardize the number of flowers to be pollinated per panicle and to assess its effect on success of hybrids in litchi. Four diverse parents viz., ‘Shahi’, ‘China’, ‘Gandaki Lalima’ and ‘Bedana’ were selected. The study showed that retention of the least number of flowers (10–20) per panicle for pollination resulted in the highest fruit set and ultimately the highest number of fruits at harvest. Large sized female flowers ensured maximum fruit retention till harvest. Fruit set was recorded as maximum in different time periods of pollination, which indicated the effective pollination period in ‘Shahi’, ‘Bedana’ and ‘Gandaki Lalima’ to be 6–7 AM, 6–9 AM and 6–10 AM, respectively. The seed weight was significantly reduced in the progeny in all crosses where ‘Bedana’ was used as the male parent, but pulp content increased, indicating the metaxenia effect of the ‘Bedana’ cultivar on fruit characteristics. Low temperature during pollination enhanced fruit set in all the crosses, thereby establishing a negative and significant correlation among these factors. This information would help litchi breeders to select the best parents to be involved in hybridization programs, getting a higher number of hybrids and selecting high pulp content. This technology of retention of 10–20 flowers per panicle during pollination will increase the number of hybrid seeds, and this technology may boost hybridization programs in litchi.

A sapota varietal experiment was conducted under rainfed conditions for 15 fruiting seasons (2003–2018) with three phases of 5 years each with varieties: ‘Murabba’, ‘Cricket Ball’, ‘Bhuripatti’, ‘Kalipatti’, ‘Jhumakiya’, ‘Mahayoti’, ‘PKM-1’, ‘DHS-1’ and ‘DHS-2’. Based on the initial five fruiting seasons (Phase I), ‘Murabba’ and ‘Jhumakiya’ were found to be promising, while in Phase II and III, ‘Murabba’ and ‘Cricket Ball’ had significantly higher yields. The cumulative yields in Phase I correlated poorly to overall cumulative yields (2003–2018). However, yields during Phase II and III strongly correlated to the overall yields for sapota varieties. This showed that recommending a sapota variety based on 10 years of data is equally effective as that of 15 years, indicating the scope of shortening of varietal recommendation duration. Our study also indicated a significant increase in the fruit weight and pulp content (%) with increasing tree age. ‘DHS-1’, ‘DHS-2’, and ‘Murabba’ produced the largest fruits. The pooled data showed that sapota variety ‘DHS-1’ and ‘Murabba’ had significantly higher pulp (%). The variety × phase interaction was also a significant source of variability among all characteristics except for number of seeds, TSS and acidity. The stability analysis based on regression coefficient (bi) revealed that all the sapota varieties had a stable yield with a regression coefficient near to one. After the evaluation, it was found that ‘Murabba’ and ‘Cricket Ball’ performed best among the varieties compared and is suitable for commercial cultivation in the East India Plateau (EIP) region of India.

Canopy architecture is one of the most critical components influencing photoassimilation, yield and quality of fruit crops; thus, it is logical to optimize suitable canopy form with high light interception efficiency. In this study, the effectiveness of three forms of canopy architecture viz., open centre, Y trellis and espalier were assessed, under high density planting system of mango (833 plants ha− 1). Y trellis facilitated better availability of photosynthetic photon flux density (PPFD) in upper (793 µmol m− 2s− 1) and lower canopy layers (487 µmol m− 2s− 1) by exhibiting moderate interception of photosynthetic active radiation (PAR). Y-trellis also manifested relatively higher photosynthetic activity (6.07 µmol CO2m− 2s− 1and 5.24 µmol CO2m− 2s− 1), stomatal conductance (0.194 µmol H2O m− 2s− 1and 0.172 µmol H2O m− 2s− 1), carbohydrate and protein content in upper and lower canopy layers. On the other hand, espalier system demonstrated high rate of PAR interception and low photosynthetic activity. Mango canopy with Y-trellis and open centre forms provided better results in terms of flowering intensity and fruit yield. Fruits from Y-trellis exhibited relatively better colour attributes, sucrose and β-carotene content. Alternatively, soluble solid contents, citric acid, carbohydrate and protein content were unaffected with the training systems. It was evident from PCA biplots that Y-trellis had close proximity with light intensity, photosynthetic characteristics, flowering intensity, yield, and fruit quality attributes. Moreover, path coefficient analysis indicated that PPFD, iPARand photosynthetic rate (Pn) were the most important predictors for determining flowering in mango. The findings of the present study demonstrate that optimized canopy architecture is instrumental for effective utilization of radiation energy for higher flowering intensity, yield and fruit quality in mango. Economic assessment of training system indicated that Y-trellis was more feasible system when cultivation was aimed to maximise the profit with no restriction on investment. However under capital constraint situation open centre system was more profitable.

The present study was carried out for 2 years (2018 and 2019) to evaluate 30 genotypes of litchi for tolerance to fruit cracking. Results revealed that fruit cracking varied from 0.00% to 16.31% in the studied genotypes with maximum in IC-0615602 (16.31%). Out of 30, 17 genotypes (IC-0615585, IC-0615587, IC-0615588, IC-0615590, IC-0615591, IC-0615592, IC-0615593, IC-0615595, IC-0615596, IC-061599, IC-0615603, IC-0615604, IC-0615611, IC-0615613, Coll. 36, Coll. 37 and Coll. 38) were free from cracking. Fruit cracking was positively correlated with fruit surface temperature (0.87), leaflet interval (0.67), and rachis length (0.48) and was negatively correlated with peel thickness (−0.84), spongy layer (−0.88), fruit pressure strength (−0.71), and number of leaflets (−0.68), which can be used as markers to identify the tolerant genotypes. Cracking tolerance genotypes can be exploited for further genetic improvement in litchi. Based on leaf characteristics (number of leaflets, leaflet interval, rachis length), seedling populations can be screened for fruit cracking tolerance at the nursery stage, and large population may be avoided.

The effective pollination period (EPP) was studied in three litchi cultivars. viz. Shahi, China and Bedana, with the objective of evaluating the best time of pollination for all cultivars involved in hybridization. The pollen grains of the previous season stored at low temperature (−20 °C) along with fresh pollen grains collected during the current season were used in the present study for pollination. Results revealed that the EPP reported in Shahi, China and Bedana were 6–7 AM, 6–8 AM and 7–9 AM, respectively. Though maximum fruit set was obtained in Shahi × Bedana and China × Bedana using fresh pollen grains (0.24 to 0.81%), an appreciable amount of fruit set was also obtained from the old stored pollen grains (0.23 to 0.52%).

To examine the microbial cooperation in the rhizosphere as reflected in terms of growth response of young trees (< 5 years) of litchi (Litchi chinensis), field experiments were conducted during 2012–2015 at ICAR-National Research Centre on Litchi, Muzaffarpur. The microbial inoculants consisting of arbuscular mycorrhizal fungi (AMF), Trichoderma viride(TR), Azotobacter chroococcum(AZ) and Bacillus megatarium(BM) along with their combinations were compared with application of recommended dose of fertilizers (RDF). The data revealed that AMF in combination with other microbial inoculants resulted in significantly higher increase in growth parameters viz., tree height, tree girth, tree spread, leaf area and leaf chlorophyll content. Growth response produced by combination of AMF + AZ + TR were the best or statistically at par (p= 0.05) with AZ + TR for most of the parameters. Similarly, significant higher root biomass, volume and density were observed with application of microbial inoculants. While AMF positively influenced the increase in population of T. virideand A. chroococcum, it negatively influenced the increase of population of B. megatariumwhich corroborated with the observed growth response of litchi trees. Thus, the studies not only confirmed the positive response of AMF and A. chroococcumreported in different crop species but also demonstrated a synergistic response of AMF with A. chroococcumand T. viridein litchi under field conditions.

Litchi is a sub-tropical fruit crop with genotypes that bear fruits with variable seed size. Small seed size is a desirable trait in litchi, as it improves consumers’ preference and facilitates fruit processing. Seed specific transcriptome analysis was performed in two litchi genotypes with contrasting seed size to identify the genes associated with seed development. The transcriptomic sequence data from seeds at mid-development stages (16–28 days after anthesis) were de-novo assembled into 1,39,608 Trinity transcripts. Out of these, 6325 transcripts expressed differentially between the two contrasting genotypes. Several putative genes for salicylic acid, jasmonic acid and brassinosteriod pathways were down-regulated in seeds of the small-seeded litchi. The putative regulators of seed maturation and seed storage were down-regulated in the small-seeded genotype. Embryogenesis, cell expansion, seed size and stress related Trinity transcripts exhibited differential expression. Further studies on gene characterization will reveal the early regulators of seed size in litchi.